If you try the Cannondale mounts (my 1st choice), it would probably work best if your downtube is close to the same diameter the bosses were designed for. Chances are it's close enough, especially if you use the plastic boss instead of the metal one.
Friction welding doesn't sound doable on a tube.
Last edited by Homebrew01; 04-10-12 at 10:30 AM.