Scott - try this:
http://www.daemon-tools.cc/eng/downloads - you want the Daemon Tools Lite product.
I've never used it with games that needed a CD, but it will let you mount an ISO as a local drive from just about anywhere. You should be able to mount it from your NAS, no problem.
Since it's a free tool, it does try to push you in to downloading some of their commercial products, but once you get past the initial pushy stuff, it quietly serves up ISOs like it promises. I've used it at work and personally for a couple of years.