I had a heck of a time finding a light mount that fit 31.8mm bars. I wound up going with this mount from Ti Cycles, because it was all I could find that worked with my canti brakes. More than I wanted to spend, but it is a nice mount, though. With some ingenuity and some old reflector mounts I'm sure you could rig something similar cheaper, though.

Another option is the stem spacer mount. Peter White has them. I don't have any experience with them personally, but they look like they might be a good fit for your rig with the Bar Mitts.

TIP: If you go the Ti Cycles mount route, don't wrap the bars until you install the mount!

I do like having a light mounted up high. The fork crown works well, but there is something nice about having the light up a little closer if you have the bar real-estate for it.