I use this solution to slow down cars for my son, but i'm guessing the problem he has is the kids use a certain radio that is easier to use for them?

I would just equip the two receivers with velcro tape, so they can easily be switched out. Just pull off the receiver and insert the two connectors, should be quick enough. I would prefer this myself over wiring up some monstrosity of y cables that allows either to be selected.

Another idea : mount both receivers, and if you have a receiver box, solder up a homemade 4 port connector bay hooked up to both rx and coming out of the receiver box. All you would have to do is swap the two connectors, which now can be done outside the rx box, and still protect the rx's. But i guess i'm back to lots of wires again, with less ease of use!