There is a thread on TGR about this, its got pictures and everything, use the search bar..
Its not an easy task, takes several hours the first time you do it and if you want to do it cleanly, you have to remove the brakes completely from the baseplate and bend them using a vice and a blowtorch(optional but really helps bend metal). The spring is a real bitch to put back in if you dont have the trick.
You know you can order brand new baseplates + wide brakes from rossignol for like 50$...