I was thinking in something like this. I did it at work in 10 minutes, so not a lot of considerations on additional aero variables, but I think that with that arm length, it is a bit outside from the flow (as in the Subaru XT mentioned by aerohead). I'm not a designer nor an aerodynamic expert, I'm just a chemist which is a bit bored at work, so this was the best I could do (I know it looks like an elementary school drawing).
I thought on this design because of the Laws on obligatory side mirrors, so they can be further optimized if it didn't have a mirror, just the camera. I only took into consideration achieving the minimum frontal area possible.
The arm can be changed to a very slim one, but I'm taking all the cabling into account.
