FWIW, all three of the All-Star resorts have rooms available on Christmas Eve. Those may be cheaper than Saratoga Springs studios and still serve the "throwaway" purposes. If they were going to MK on Christmas Eve, they would not need to check into the rooms first. However, I don't know what would happen if no one checked in on Christmas Eve and they tried to go to Early Entry on Christmas Day. Disney might consider the reservation abandoned and cancel it if no one ever checked in on its first day. Maybe someone else can answer that question.
P.S. The All-Stars all have rooms available for check-in on Christmas Day also. People checking in that day can attend Early Entry that morning.