This will only work if you delete the title update (AKA the thing that patches your cheats and stops them working).

If you get four controllers on, only sign into one profile.

Start Dead Ops, then have the 4th controller sign in right when the game starts.

This will take you to the main menu of Black Ops, go to Nazi Zombies, splitscreen and the screen will say "Players in party 2/4".

Start the match and boom you got 4 player splitscreen on one console!