My personal technique is one that doesn't allow any of the removed part to be salvaged.
1. Drill a hole through the top of the shell with a dremel (pin drill might work).
2. (optional) Wallow out the hole by eating away at the body with the drill bit.
3. Whittle away the remaining plastic with CAREFUL cuts, and a #11 blade.
4. Finish with files.
I'll be the first to tell you it's a risky technique. There are plenty of chances to make a mistake, damage the shell, or even take your thumb off. If you're careful, it works well, though. Since I couldn't get fancy tools as a kid, I got plenty of practice with this. ...Just the other day I used the same technique to mount a switch in the dashboard of a vehicle.