Yeh you did say "helmet" and not glasses mirror.

I eventually wound up coating the back side, around the stub and wire, with JB weld. I don't recall if I needed that to secure the wire, or if it just looked better, but from my image date it's held up for two years.

I do recommend the twisted wire btw, over anything stiff like a spoke or plastic rod. If you do crash it will bend out of the way without poking or scratching you, and there are no pivots to wear out.