Hmm. This is kinda what I was looking for:

http://www.batteryspace.com/helmetmo...t.aspx#reviews

I'm not sure about that negative review. As a part of a bike commuting incentive, I received a little flashlight and one of these mounts to mount it to the handlebar:

http://www.batteryspace.com/mounting...elighting.aspx

Looks like the same clamp design. While I wouldn't rely on it for the handlebar, a helmet mounted light is subject to a lot less vibration and shock. Worth a try, I guess.