I've done technology mentoring for several years now on the side. I've found that you have to be co-located for it to work effectively. It's one thing to be a voice on the phone or an icon on IM, it's something else entirely to drop by for lunch, take a look at the build, and roll your sleeves up and pitch in. That's a face-to-face kind of thing. As another commenter pointed out, a lot of people don't feel like they need any help. Those that might entertain the idea want to see that you can walk the walk and not just talk the talk -- which is exactly as it should be.

So I'd look locally if you can.