I run a Tektro BMX lever quite happily. However, it's true that it was too small to fit my bars. So I did what I seem to always do and got out my #1 mechanic's tool: a 5lb claw hammer. I put a wedge in there, drove that bastard open, and slid it right on. Then I got out the vice grips and clamped it down on the bar so it mostly fits.

The screw holes don't line up anymore, but that's actually cool because I have a few degrees of motion if I want it in a slightly different position (which is more often than I would have expected, strangely enough).

The brake works real nice and the short two-finger lever stays out of my way except when I need it.

Note: I removed the vice grips after squeezing the clamp together as best as I could. I am not, repeat, am not riding around with a vice grips protruding from my bar.