Shimano Ultegra bar end shifter mounted on a Suntour thumb shifter mount.
I have both of these lying around. Cheaper than Paul Thumbies fo' sho. But when you read the fine print he states that: "I didn't say it was easy. The base of the Shimano shifter has to be prevented from turning. I drilled and tapped the bases and ran screws throgh the back of the mounts."
I'd prefer the Tumbies though because I can mount it between the brake lever and the grip. http://paulcomp.com/mtthumbie.html