[Arkan1k]

You could just use the "0/Ins" on the numpad.
As simple as moving your pinky finger across and holding it down.
I also like Kai's idea of locking onto a particular player. Then by pressing left or right you circle the selected player and by pressing up or down you move further away or closer to the selected player.
That would work very nice.
But then I guess it comes to the fact of firing. You would need to change the shoot to shoot towards the selected player instead of just shooting in the direction you are facing (playerdir).