this might be helpful for your situation... it's a product called AVCast from Crossbarmedia. It uses the 'unused' portion of your coax to xmit the IR commands thru the wires. It's main use is to create your own media network in your home, but the IR functions are outstanding. i've used these at my house for years and had very good results. and it does come with the little stick on xmitters so you can 'isolate' where the signal goes. hope it helps!
reVx
http://www.crossbarmedia.com/html/media_kit.html