Well, to be honest, it would be possible to do that if it weren't for one thing. Black Ops 2 does not have built-in code for co-op in the regular version of the game, unlike MW2 (which has a co-op mod based on special operations within the game) or Black Ops 1 (which also has a co-op mod based on the zombie mode within the game). Black Ops 2 does not have a built-in zombie mode in the game, as the zombie mode is essentially a separate game that the regular version transfers us to, so in essence, it is three different games in one package. Multiplayer, Zombie and Campaign run on different .exe files. And technically, it is not possible to make a mega co-op mod for the company.