Has anyone ever used a modulator to inject a DVR video feed into a distributed coax cable TV network?  I have a potential customer who is wanting to add their DVR footage to an unused channel.  They have a basic cable TV service from the local provider which is connected to 2 televisions in the office area.  There are no cable boxes or converters in place.  The coax that comes from the outside source is split and then runs directly to the televisions.  I'm wondering if its possible to pick an unused channel and somehow inject the video signal from the DVR into the coax on that available channel.  If this is possible would it be available to the other cable TV customers in the area?  My customers can come up with some interesting requests.