Update: So after thinking of the best way to go about it for a week, I decided to just take the risk, and cover my right shoulder in craft foam. I only had one shot at this, as I had to especially buy a single XL sheet of the stuff to prevent any seams. With alot of heatforming, I was able to get the shape right but there were folds. I had to resort to making cuts, which I really didn't want to do, but I've started caulking the seams and I'm confident I can make it work. So I glued the whole thing down and pretty much got it as smooth as possible.
As you can see I've cut out 4 slots that got covered by the craft foam, and sanded the edges down to clean them up. As for the 2 circles, I've decided to just use black screw-covers, as they look alot neater, and I've had a bad experience trying to cut circles. I'll buy some of those soon.
Next up is to do another layer of caulk to finally smooth those cuts up. Then I can clean up the outer edge, add the few details, and I'm done.
EDIT: Aw crap, double post. Sorry about that, especially considering I'm usually the one telling others not to do it.
