[Cd]

Here is the mirror folded back - actually I'm holding it because I flipped it back so many times i broke the spring mechanism.
The blocky piece on the mirror itself is an aftermarket fisheye mirror . the stock mirrors don't have this appendage.
If you look at the shape from the side and especially from above, it almost seems designed to be folded back for good aero.
Perhaps a trip strip could be added along the back to make it even better ?

I can imagine a servo that would be triggered from within the car at the flip of a switch. ( to move the mirror flush. )