My boyfriend is doing this as well - but I told him that since everyone was going to do it, he should do it differently. We settled on the scene where he's dressed as a nurse, same makeup though.
I'm going to use sponges to put on the grease paint, so it hopefully dries out easily and cracks a bit. I think the key is making it soft and messy (no harsh lines) and we are going to experiment with this fake scarring stuff we bought. Now that I think about it, I'm going to try using a light dusting of powder over the grease paint and see if that makes it flakier.