BSR's solution is the simplest by far; however it can be hardwired as well; I personally have always ditched the smart control in favor of a regular button - so in that scenario, you could have multiple simple buttons; or you can run the wires from the new button back to the original button and solder to the same terminals that the button connects to - that way it's just like pressing the button on the smart remote.
However, I'd still just Velcro a remote to the other wall.