I made a ghillie cape last summer and find it's not to bad to crawl around in. It is just a rectangle net with some burlap straps so you can put the cape on like a backpack. There is also lots of net above the shoulder portion so it can be pulled over as a hood. I used jute twine for the majority of it, but end up cramming the ghillie full of grass, leaves and twigs to make it effective.
I think the easiest thing to wear under it is a belt with a few pouches. CIRASs are too big. But if you really wanted to, you could put this over your CIRAS.
http://i222.photobucket.com/albums/d...o/DSCN5066.jpg
http://i222.photobucket.com/albums/d...o/DSCN5033.jpg
http://i222.photobucket.com/albums/d...o/DSCN5029.jpg
http://i222.photobucket.com/albums/d...o/DSCN5030.jpg