So I bought a couple of ubercheap wide-angle mirrors that stick on to the sideview mirrors and was fiddling around with them. They are about the size and shape of my thumb which for the wide-angle function seemed fine. But I really didn't want to stick them on the mirror itself, looks too tacky.
Then I got the idea of clipping them onto my macneil rainguards - on the inside at about eye-level so they wouldn't be obvious to anyone outside the car. But they weren't quite the right shape and where a little too big. But it got me to thinking that there might be some out there that are designed to clip on to an edge rather than stick on top of a bigger mirror. Anyone see something like that?