One of you go to the ledge above the lift while the other is one the lift.
The person on the ledge must now try to jump on the person's head (so you are standing on the head of the person, on the lift)
Now wait and you would find yourself float up past the roof (to some sort of shaft), but still able to shoot. Just fire down with whatever weapons you have and ENJOY the kills (of the Dark sims)
NOTE: MUST have Dark sims set against you so they can flock around below you and your human player)
Go to the toilets and hide behind a door and when the sims try and open it blast them away by shooting through the door with high velocity bullets!