I discovered an easy way to mask an area using the painter layer. I was trying to mask a very large area which was being covered by 3 projectors (Each one was a different model)
using a triple head 2 go. I realized that taking photo's from each projector location was going to be a nightmare in photoshop later. So, i used the Painter layer to paint my projection area white, then render output as a PNG. Once PNG was imported into Photoshop preparing Mask was very quick because it was black + white.
I think this would be even easier with a wacom tablet, i will invest in one me finks.