You could run a simple AB box. Run both receivers into the AB box and a single line to the motor. Now you are assured only one box at a time can control the system BUT you will only be able to use one box at a time unless you actually devised some schematic utilizing loop out on each receiver so that if you were on A receiver 1 would control the system and through it's loop out you could run a DC pass on one leg splitter into the other receiver and the reverse out of the other for when B was activated. It is late so I am not thinking all straight right now as to how to wire all this to make it work correctly without potential damage to the other unit.
It is conceivable to do though in my mind at this hour
