I would also recommend the GT3b. They have a couple of mods you can do to make them better also. If you really want to go down a rabbit hole, there used to be a couple places that made adapter kits to flash after market firmware to them to add all sorts of functionality to it, but I thought that...
I'm not aware of any way to do it. From what I can tell, once you bind the TX to a new RX, it becomes unbound from the previous RX. I would also recommend the GT3b that WF posted a link to for a decent, inexpensive multi memory TX. Let us know if you figure it out.