David,

You've covered most of the options. I do have a mirror which attaches to the bars with a loop around rubberband and a hook. It is quick on and off and has a bit of pivot up and down. Adjustment is a combination of placement and the pivot.

It is called the Zefal Spy Bike/Handlebar Mounted Mirror and is sold by Nashbar. While the pics show it at the end of the drop, it can be placed in several locations.

I find, however, that I cannot use it as safely and efficiently as helmet/glasses mirrors.