You can still use DME!!!
There is absolutely no requirement that you actually fly into or out of MCO.
No matter how you get your body to MCO, you are still entitled to a Disney's Magical Express ride from MCO to your resort on or after your check-in day.
This is a fact, but not all CMs you'd talk to on the phone will know this, or will be able to handle it without putting you on hold for 20 minutes to figure it out. To save yourself the bother, I suggest you look at flight schedules and tell DME you'll be arriving on a flight from wherever at about the time you expect to be at the airport.
To help you with luggage, let me suggest you drive to your resort first and drop-off your luggage, and then drive to MCO to drop-off the car and take DME back to the resort. This will save you from having to lug your luggage from the rental car drop-off site to the DME counter.