Fastest way I found to do this is make the gamemode elimination only. Only takes 3 kills to win. Choose the map Garden. When the match starts change the 2nd controllers weapon to grenade launcher by pressing RB twice and then A. Turn around and shoot grenade into corner and kill yourself as the 2nd controller to commit suicide 3 times. When the round ends press Y to get to the next round. Do this for 20 rounds.