You don't give them any flight information.
You tell them exactly what you're doing, and around when you want to return to the airport to get a ride to your Disney resort, and they'll make the arrangements.
HOWEVER, make sure you make these arrangements with DME directly at 866-599-0951. The people answering those phones are DME cast members, experts in how DME works. They'll take care of you. The second HOWEVER is you need to wait to make these arrangements until you're no more than 60 days away from your trip. DME reservations are only possible if you have a Disney resort reservation, and the DME folks don't have access to the resort reservations data that is more than 60 days into the future. So they can help you, but they can't help you any earlier than 60 days before your arrival.
Please don't bother calling 407-W-DISNEY about this matter. More than likely, if you call there the reservation agent will give you the very wrong information that you can't use DME on the day after you fly into Orlando. Yes, you could research MCO flight information and tell them a white lie of a flight number that arrives around the time you want to leave the airport ... that would work, and it wouldn't do any harm, but it's an unnecessary step for you, it's effort you simply don't need to put out.