Another possible alternative, with less work and possibly less $....
Measure your current set of V-brake arms to determine their length. Higher end/more powerful units sometimes use longer arms for more leverage. See if a pair exists that will provide you with the clearance you need.
Check the Avid Ultimate line, also the Nashbar Deluxe (rebadged Tektro) V-brake. I bought a Nashbar set and noticed the arms are longer than a set of Shimano M420's and Avid SD-3's.

If you need A LOT of clearance, then this route won't help you.