I guess it would be rather easy to implement a kill streak system with skulls. First you would have to remove all "add yellow/white/green/red" skull. Second you would have to remove all effects from skulls, 100% item loss with red skull for example. Then you would have to remove "check if the player you killed was skulled" so you always get an unjustified kill. Also you would have to remove the frag count down and instead add "remove all unjustified kills" when you are killed/respawned. Finally you would have to add more skulls where 3 unjustified kills gives you a red skull.
Problem is, I can't compile because I haven't got the project. I don't know if the guy Gail payed for the server/compiling is willing to implement all this for him.