I think I'm gonna use one of these http://www.dccontrol.com/0820.htm
I wired one of these to the high speed and used a relay for a manual override (in case the DC one ever fails out in the tail; so far, through, it has worked like a charm!). So I have AUTO/OFF/ON on mine. I also got the LED light to be able sse when the fan is on, although it is not as usefull as I thought it would be (my understanfing was that green was for when it came up low, oragne in medium, and red when it came on at high speed, but in reality, green is off, orange is on at low speed, and red is a little faster speed, but not much different).
Felipe