Doug:
You could use programmabe UHF modulators... set the outputs to whatever channel you want. We use them on the ship for the "cable system" we built. They work pretty good.
Here's some on this page... it looks like some of them can have at least 3 inputs, and also output on 3 channels at once. That's kinda neat.
http://www.futurehomesystems.com/v100.shtml