CAP is just volunteer flying, thats all. Its completely un-compensated. That being said, I think the best piece of advice before flying anything extra is to let your company know what your doing. If they say no, then so be it. However, if you do it behind their backs you're probably not going to be given the benefit of any "grey" area.

I know, I know, this idea seems a little too much "kool-aid" like, but I doubt any union will provide any protection for items such as this.