+1 for the Stebel Nautilus (?). I split my compressor from the horn bell and mounted to in the fairing on the rt side next to the headlight. The clamp for the compressor is about a perfect fit for the fork. A couple of zip ties (black of course, don't want to look like a hill-rod) and some black silicone to be sure. Ran some clean vinyl hose between them and watchout!! As an added bonus, the horn leads are right there, close enough to power the relay to control the whole thing.
Best thing is when students ask me what that black thing is on my forks, I get to show them. (hehehe). ;-))
If you need to see a pic I can take one in the morning, it's a little late to go out to the garage tonight.