I'd like a system like this:
Looking forward, you hit '2' on the numeric keypad (or coolie hat equivalent): you look behind/high (45°)
Looking left, you hit '2' on the numeric keypad(or....): you look above your left shoulder (like our 6 view now, but with the point of view offset to the left)
looking right, you hit '2' (....): you look above your right shoulder (....).
So with 1 button, or 1 coolie hat position, you have 3 ways of looking behind you, depending on where you were looking the instant before.