I remember back in the 80's when cable ready receivers were making their debut and the cable company didn't take kindly to multiple in-house sets but I'm surprised to hear that mentality is still around today
I was doing some searching this morning before I stumbled upon this great thread and discovered "multi-channel" RF modulators capable of transmitting 2, 3, even 4 or 5 channels simultaneously over one coax, all from individual component inputs. The whole thing is digitally set up so you can configure the inputs to whatever channel you'd like, but it's a pricey affair at several hundred bucks.
Guess where I found it? None other than an audio/video security site, likely targetted so you can check multiple cameras over your in-house cable system. Just add digital converters (and maybe a dvd player for an in-house classics channel of your own) and you're set!