Thanks D-Man, I checked there also, but looked again at your link. I don't know the dimensons, but the shoulder on the backer the stud screws into looks deeper than the hand guard is thick and I'm not sure the bipod could tighten down all the way. They do have one intended for A2 hand guards that looks like it might work, but I'm concerned the stud will slide around in the hole over time.
Now that you mention the g2, it would be pretty easy to drill and tap, but the only place with enough meat is right at the end of the rail, and it's a 15" on an 18" barrel. The legs of the bipod would be sticking way out past the muzzle. I would mount it to fold back, but then there's no loading the bipod with a harris.
One of those harris adapters and some sort of washer modified to center the stud in the hole is probably what I'm thinking now.