I realize this doesn't answer your specific question. However, have you considered a (sun) glasses or helmet mounted mirror? I use a "take a look" brand mirror and can't imagine using anything else. It took me years to talk my wife into trying such a mirror, and now you couldn't take it away from her.
@Hillrider, I do remember them being sold here too, but now all you can find is the ones that can mount at the ends of the bars.
@Old Hammer Boy, although I've never tried using a helmet mirror, I'm always open to new ideas!
...so basically I've discovered what you've both suggested on eBay, and they're cheap enough to have ordered both!