So I clipped another curb with the Toyota this weekend and gashed up the rim >:-( ...luckily just moving off (it was a really nasty 120deg+ corner on a 1.8 lane wide road). It got me thinking about rim repair again. I've read all about it and bondo is typically used as filler. The problem is I don't know how those will hold up in a tire shop. I got to thinking on other, harder fillers. Hot rod guys like to use lead as a body filler, but I don't know how that will bond to a rim (or affect its balance). What about JB weld? Just as easy to apply and dries hard as metal. So I did some research:
http://www.airforums.com/forums/f381/body-filler-j-b-weld-or-us-chem-all-metal-44606.html
http://www.thirdgen.org/techboard/body/274297-jb-weld-body-filler.html
http://www.hotrodders.com/forum/jb-weld-stuff-70570.html
http://www.honda-tech.com/showthread.php?t=357912
TL;DR version: JB weld is very inflexible - that's a plus on a rim though - and there are some concerns about workability and paint adhesion, but it looks doable. Anyone tried this?
BTW if I don't reply in a long time it's because I'm trying to get a hold of a cheap, freshly rebuilt blacktop I just found on the local boards! 
I've never tried JB weld but so far the bondo I've used is holding up well 3 years later and I've had tires mounted on the rims 4 times. Guess it depends on the tire machine.
I've done it; works well but it was a bit soupy so I had to use masking tape to hold it in place until stiff, then work it down to match the surrounding rim edge profile. The rims have had two sets of tires mounted without issue.
Re: paint: This was on a set of beater rims for autocross that I never took great care of after a hasty paint job so I can't say if a more carefully applied paint would hold onto the JB Weld. I assume their website has instructions on paint prep.
One thing I would do if I re-hab rims like this again is make a spindle on which to hold the rim so it can spin freely while working on the edges. (The spindle would hold the wheel horizontally, like a potter's wheel.) At a pro wheel repair shop I once went to they use a machine that spins the wheel (it may have been a standard wheel mounting machine). Also, they used a pretty aggressive flapper wheel on an angle grinder to knock down the jagged portions of the curb rash, leveling it with the undamaged portion of the edge. I did this, too; it works well, but be careful because you can pretty easily remove more metal than you want with a flapper.
