It seems to me that building a retractable system to bolt to the beams would not be all that difficult. They could include a linkage to turn them sideways as they are pulled up. The design in my head suffers greatly though when such a wide tire is required. It seems it would have to weigh at least 50lbs.

It may be worthwhile in a setting like yours with a frequent need for wheels in a hurry, or in a point to point race that requires transport over land in the middle.