I think 'Wabbit Hunting' is a nice idea, though I have a suggestion. Let's say Max Score is 100. When you kill a non-target, you gain one point. Doing so 5 times will result in a penalty (let's say not moving for (x) time). Killing the target will earn you 10 points. The target should always have a recognisable character in his or her name (like the asterisk for the CTF flag carrier).

Having that penalty, people will be encouraged to find their targets instead of going on a rampage, but when you do kill someone who isn't a target, you won't be entirely let down by the lack of points gained.