Yes you can.
What we did last cruise and will do next is 2 nights at WDW, then evening before the cruise departs (after the day relaxing at the resort after checking out) take ME to the airport and check into the Hyatt in the airport. In the morning Hyatt handles our checked bags, so we only have to get ourselves and carryons down and onto the bus. We get in the informal line before the formal line starts at 9ish. Last cruise we were first family on the second bus leaving.
We find this works well because the transfers are broken up -- evening, get in, check in, maybe take a walk around the airport and hotel, then to bed. get up at a not quite insane hour, get ready, have breakfast at the Hyatt restaurant Hemisphere (or in the airport food court), one last pass in the room, then head to the line for the bus.
Leaving from WDW, doing ME, then the
DCL bus all in the morning means an early wakeup, early breakfast, early bus etc.
As for ME, they will let you book without a flight. You just tell them you are returning to the airport to get the DCL transfer and want to be at the airport for about X time. If the CM you are speaking to does not know how to do it, ask to speak to someone else.
SW