I have recently purchased an RF to RF converter for this purpose. It is available from
http://www.myelectricdog.com/ You need to purchase the multiboard, a 418Mhz receiver and a 310Mhz transmitter. You will also need (not available here) a 5v regulated power supply and possible two antennas. It works really slick. I am also trying to control my ceiling fan with a second transmitter mounted on the same multiboard. I have been having some problems with that part, but Dave Houston, who's son runs the above website, has been an excellent resource and has provided ample help!