Thanks for the gauge info, O-Cha (and others).
And generally speaking, thanks for the input so far, guys. Fantastic ideas I had not considered.
I am going to contact the mirror guy because, quite frankly, that's the perfect solution for me, assuming it doesn't cost me my ass. The mounting solution has to be semi-reasonable, although I am well aware that I'll end up getting what I pay for in most cases. If I can swing it...
Totally willing to go a week or two without a rear-view mirror. Might be able to find one on craigslist or something if I decide to go that route (which is, essentially, pending only price).
The sunglasses holder idea is still a solid one, I think, especially if someone has a form made. With that, you can just send it around the boards to anyone who wants it, and any competent fiberglass or carbon purveyor can use the existing form to do a one-off for a reasonable cost.
The heavy lifting is the form. If I end up going that route, I'll be sure that my purchase agreement includes the form. Then I can just share it as needed.