I've built a small demonstration control that I call the Retro Transformer. It uses a panStamp radio board in a box with a few switches, pushbutton, and a potentiometer. The switches cause the panStamp to send simple "transformer" operations to an engine (via the TIU) over the radio.
There is a video and short description on my web page:
http://www.silogic.com/trains/...Radio%20Support.html
Mark