If this isnt possible the second best thing to do would be to remove kills from the scoreboard completely.
That way, the greed to get kills will decrease. People will step aside and let someone more suitable of making the kill do it.
Teamplay will increase and th/tk will decrease. Instead reward players for winning rounds.
Maybe start to keep track of the round wins and losses and show an average win-loss ratio on the scoreboard instead of the kills?
People with higher W:L ratio will get more respect and maybe they should get special privileges like some new commander system.
This will increase teamplay.