The most i would do is ask his mate to put in a good word for you one of their general conversations, then ask his mate what your crush said, and then do the rest yourself.
It does depend on what help you want! i'd totally like to know what the guy i like really thinks about me, but if someone starts bringing me up in random coversation or fishing for his opinion on me, then the mate might give me away - some people aren't very tactful!