I've never done anything like this before, but I was wondering whether it is possible to take pre-recorded video, say in wmv format, and convert to wtv, place them in a Windows Media Center folder, and have it display in WMC when recorded TV is selected. My goal is to have friends record a birthday greeting for my roommate and have him see it when he tries to watch the evening news.
This is probably much too late for your project, but from my research into the WTV format, VideoReDo gives you the ability to edit and create WTV files. I have not used the program itself as it does more than I need, but might suit your needs.
FYI - it is NOT free, but there is a free trial that might let you do it.