Go to the theatre and link the teleporter, then teleport.

When you get back to the lobby, go upstairs, turn on the trap and camp until the trap turns off.

Make sure there is at least one crawling zombie following you. Don't kill it and wait for the teleporter to cool down again to link it and repeat the process.

Note: you want to have a good pack-a-punched weapon to survive longer, I survived to round 21 alone with a Porter's X2 Ray Gun and a Skullcrusher.