As you might have guessed, play on the easiest difficulty and rush like hell. Skip as many enemies as you can. If you have played any of the Call of Duty Zombie games, you will be familiar with what is called a "Rape Train". Get a large amount of enemies to run after you and when they are all bunched together, take them all out as a group to maximise firepower. You of course can't use guns, but you can use your knife and powers. It will be much easier doing this with a character that is a higher level since it will mean you have more health and more points spent on your powers.
In solo play, complete a level without firing your weapons once