Yup. I've been using the splitter trick on network runs for about 12 years now. Works great. Works on the principle that only four wires out of the eight are actually used for a given ethernet run, so you can gang two network connections on a single cat-5 cable. Sometimes I use pre-made plugs for the purpose, sometimes I use hand-made breakout boxes.

In the particular instance that I described, where I already had two ethernet plugs in use, those two plugs just happened to be *already* from a split. I had run only one ethernet wire from the router in the basement up to the AV rack in the living room, and split it at both ends so I could get two plugs there. Adding the HR22 meant needing a third connection off of a single cat-5 wire, which can't be done with the splitter trick. My choices would have been: a) run another wire from the basement, b) put a hub in the AV rack, or c) magic faeries come to my rescue and let me daisy chain the HR22. For the life of me, I didn't expect that it actually would end up being (c).