I think I've come up with a plan - I'll know after our upcoming trip. We purchased a folding memory foam mattress from Amazon. The plan is that as the slideout retracts one person will fold up the head section and the foot section will remain in position. That way the bed coverings should all stay in place. We'll see!
The folding mattress from Amazon has three sections. By folding up the head section as the slide retracts, the rest of the mattress doesn't need to slide.
It's not the perfect solution, but it sure beats the factory setup (my opinion).