D'oh!! I just asked this same question in a new thread, totally missing this thread.
I am thinking it really comes down to what kind of mood the cop is in. If a cop pulls a person over soley because of a mirror inspection, I am guessing he/she will be writing a ticket. On the other hand, if a cop pulls a person over for another violation, like speeding or running a red light, they are probably not going to stack violations. I am going to try the convex mirror stuck on my vent just to see how it goes. If everything goes well and I find myself without doors more than with doors, I will invest in some sort of alternate placement mirror idea.