you could go the brake plate route, its used commonly in BMX, you can get them in U brake and V/Canti sizes, they just bolt on to your existing brake hole. i've used them before and their pretty strong and cost effective, and you can always just unbolt them
heres a link to Dans comp, just go under brake accesories,
they're listed at 24 bucks for the V model, http://www.danscomp.com/index-park.html
i've had one for around 5 years on the back brake of an old dirt jumping frame,
the draw back is they don't look as nice.
but, they work