You could make a a sliding scale, the more damage you do to the enemy team, without causing team damage the more of a bonus you would get, if you just sat there doing nothing the whole match and did zero damage you would get zero rewards.
It would have to be something half way tidy or people would either ignore it or not bother.
Just an idea.
Edited by Balvier, 29 July 2015 - 08:45 AM.