I can't understand why anyone who has problems with heat would go to central Florida in September, but nonetheless.
You could always go to Guest Relations for a GAC.
What is the Guest Assistance Card, or GAC?
The Guest Assistance Card (GAC) at Walt Disney World is also called the Special Assistance Pass (SAP) at
Disneyland. Both refer to the basically the same thing. The GAC used to be called the Special Assistance Pass. The name was changed to Guest Assistance Card a few years ago because some people thought it was a front-of-the-line pass, which caused some confusion between guests and cast members. Some people think there is a back door into most rides that they will get to use if they have a GAC and that's almost never the case -- many attractions have mainstream access. Always ask the Cast Members at the attraction how to proceed, and please do not expect front-of-line access.
The GAC is not used to jump the lines, it is used to help special needs travelers get access to attractions that they would otherwise not be able to see due to health, mobility, or major developmental and psychological issues. You may be allowed to bypass the lines, but you should still expect to wait. Examples of people who might benefit from using the GAC include folks of all ages and backgrounds, whether their need is temporary or permanent:
* People with mobility issues that would keep them from being able to stand in long queues who are not using wheelchairs,
ECVs or canes;
* People who are particularly heat or sun sensitive to the point that it endangers their health or safety because of health conditions such as Lupus and Multiple Sclerosis, or people who are on certain medications;
* Families traveling with special needs children or adults who have health, psychological or hypersensitivity issues that make it difficult to remain in crowded queues;
* People who are easily fatigued or in pain due to serious health problems (heart, emphysema, arthritis, etc.) who plan to be ambulatory inside pavilions and attractions but park their wheelchair or
ECV outside, or choose not to use wheelchairs. They get access to the seating without stairs in shows, for example. Also use of alternate entrances in places where the queue is not mainstream and there are stairs or a climb.
How do you get a GAC?
You can go to Guest Relations at the entrance of any of the Disney parks and request one. You don't need a doctor's letter or any evidence to show that you need one, although many people do take a doctors letter for backup. You do need to be able to explain what your problems are and what assistance you need. The GAC is not a convenience; it is a tool for access. Guest Services Cast Members are responsible for determining who will be given the GAC... it helps to be prepared and know what to ask for, and how, before you go.
How long is it valid?
If you are given a GAC, it will be good at all the Disney parks for the length of your vacation. You don't need to get one for each park or for each day. You do need to get a new card on your next vacation to WDW; it is only good for one trip.
What does it allow you to do?
The cards all look the same, but each card has different instructions stamped on. We are aware of 5 different messages; there may be more.
* Allows a stroller to be used as a wheelchair in mainstream queues and at alternate entrances. ECVs and wheelchairs can be taken into any building or line without having any pass or card. This allows strollers to use the same alternate entrances.
* Allows a waiting spot shaded from the sun if the line is "in the sun for an excessive amount of time." Fo most of the lines, the largest part of the line inside a building or under a roof or shade. Some of the outdoor lines are even air-conditioned to avoid getting too hot. This is helpful to people who are sun or heat sensitive.
* Allows an alternate entrance waiting area for people who can't wait in line. This one is mostly used for children/adults with conditions like autism, ADD or other health problems that make waiting in line difficult or dangerous for them or the people with them. This would also apply to people who suffer from agoraphobia or severe panic attacks that would make waiting in line in close contact with other people impossible. Also, this is used for people who are immunosuppressed and need to avoid infection.
* Allows front and center seating at shows, for people with severe visual impairments
* Kids at WDW thru the Make A Wish or similar organizations. This card allows "front of line" access because these kids are very fragile and have a life threatening condition. These cards are arranged thru WDW and Make a Wish or Give Kids the World as part of their visit.
For the first 3 categories, you will be asked to use FastPass if available and you are told that the card will not allow immediate access to rides/attractions. You will often still need to wait; it just may be in a different place.
Do you need a GAC if you have a wheelchair or ECV?
Maybe, maybe not. If you have a wheelchair or ECV, cane or crutches, you will not need a GAC unless you have a medical reason not to be in the mainstream lines.
If you have a legitimate reason for a GAC as outlined above, then you need to advocate for yourself at Guest Services in order to get the GAC. They may try to tell you that you do not need the GAC because the wheelchair or ECV will be enough to let the CMs at the attractions know that you need to use the accessible entrances. This is true if your reasons for being in the wheelchair or ECV are only due to mobility issues. However, if you plan to leave your wheelchair or ECV at the entrance of an attraction or pavilion and walk inside, having a GAC will alert the CMs that you need to use the accessible seating or boarding areas inside the attraction.
If you have medical or major psychological issues that would prevent you from being able to use the mainstream, wheelchair-accessible lines along with all other guests to the point that you would have to miss the attraction or it would endanger your health, then you will need the GAC.
About using the GAC when you need it...
Many people feel embarrassed, or like they are cheating if they ask for a GAC. Please don't think that using the GAC to get to alternate waiting or boarding areas is just a 'bump in' to the line... remember:
* You are paying the same as everyone else at the park.
* It will take you longer time and more physical energy to move from one attraction to another.
* You will most likely not stay in the parks as long as average guests.
* You will need to spend more time resting and refreshing in between attractions.
Perhaps other people arrive at the line ahead of you, but you have every right to enjoy the attractions at your pace. Disney has this program in place to help you get the most enjoyment possible from your visit to the park It isn't something for you to feel embarrassed or self-conscious about, when you really need it. It is not the same as a front-of-line pass, and there will be times when you may wait longer than people in the regular queue.
About using the GAC or wheelchairs when you dont really need them, to get into attractions ahead of other guests
Better not let any of US catch you trying to pull a stunt like that! Every time someone does this, they cheat everyone. It causes resentment among other guests and cast members towards everyone who uses the special accommodations for legitimate reasons, and makes it harder for people who really need the accommodations to get them.
My suggestion on top of the really good ones you've gotten so far is-- walk through all the gift shops instead of in the heat. You can make it most of the way down Main St. in the A/C just walking through the Emporium. Sure, it'll be a little more expensive 
but it helps keep you cool.
