I read your post back when it was originally posted but didn't know much about the HDHR at the time. I had just gotten it. But, your question is one I had also originally wondered about. Now, that I know a bit more I can address your post now.
No, I don't think you can use a WDTV to connect to the HDHR directly, at least not with the stock firmware. Even if you could, I don't know how you'd change channels. Using Sage software, I can access the buffer file it records on the PC with my WDTVs, however I am still stuck on the channel I set live tv to on the software. I don't see a real use for this unless I am watching something in the den, and then want to finish it on another WDTV in another room.