This cheat works for Xbox Live Nazi Zombies.

First face the help door, then turn around and on your left there is a corner that looks like it's open.

You have to sprint jump towards the part that looks like it's open and crouch and it looks like your floating.

If you did it right when you try to stand up it should say can't stand here.

It might take a few tries and if you cant get into the glitch when you run and jump, then try to lay down when you hit the wall.