I'm with Rob on this! Just remember to put a 16 - 24tpi blade on. A demo blade with 4 - 8 tpi will pull that sawsall right into the wall when it catches the nail.
A hammer works well to, if you're not concerned with the finish.
An my personal favorite for 3 gang or larger is a metalic masonary box. (Why pay less!) And lots of room too. You can park your truck in there, and the only thing a Graffic Eye dimmer will fit in.