max. tire clearance for the mavic bridges (according to speedgoat.com) is 25mm... and $25 each...

I'm aslo working on this project and am compiling a list of long-reach canti's / v-brakes, thanks to cross-posts in MTB and Cyclocross.
So far I have:

Onza H.O.'s (Onza's out of business but some of their stuff is still around - check E-bay there's one up there now and bidding's $25)

Avid Tri-align at $75

and
paulcomp motoBMX v-brakes at $125



If anyone else knows of good alternatives, please don't be shy...

also an interesting quote about the paulcomp motoBMX brakes...
"When you convert from a 26" to a 700c, drop levers will work fine,
but if you go back to 26", drop levers are absolutely not recommended
for use with these brakes; in this case you must use a long-pull lever."