Because ME wasn't available yet, officially, I used Mears shuttle on 4/23 for transportation from MCO to SSR.
On the return, I called Mears the required 24 hours in advance for pick-up the following day and was awaiting the shuttle, when a new Dis ME bus pulled up. The driver exited and asked if anyone was waiting for Mears to take them to the airport. Several of us were and he had all of us give him the luggage and directed us to board the bus. I explained I wasn't a ME guest and he said it didn't matter as long as I was waiting for Mears service.
It was a smooth ride. The bus is themed, just like Disney. The seats are upholstered in red with gold stars. The driver dropped off those guests on one side of the airport and then drove the rest of us to side B for our airlines.
I'm sure the rental car companies will be groaning but it's going to save me $26 round trip next time, let alone the hassle of handling the luggage at the airport. I think though that you're supposed to schedule ME at least 21 days in advance.