What you have to do is connect a second controller and sign in a guest. Then, have your partner do the same. Now create a public match on whichever map you want and as the countdown begins before the game starts(the actual numbers, so you have to be quick), hit x and sign out your guests before the game starts and you have your 2 player game that will record on the leaderboards.
Tedious and stupid.. I know. Just another reason why I don't like this version of zombies..