You use DME to get to your resort, then head over to the Dolphin the day before you need to get to port. You can do that on an Epcot or DHS day...that's what we do. If you aren't using
Alamo/National, you can head to DTD and use one of the car rental companies that are based in the hotels in that area.
Budget is located at the Doubletree and will actually send a car for you to get you to their office if you want.
Just a thought.