Alternatively, you could begin a splitscreen private game of single round Scavenge, on the Dead Centre map. Use your second controller [the guest] as the survivors and get them to stand at one end of the small highstreet section. Then, you [playing as the infected] should throw yourself at them and allow yourself to die until you spawn in as the Charger. All of the Survivors should be grouped together pretty tight, as the AI character's will clump in around your 'Guest' player. Charge them, and, with enough luck and skill, you should bowl them over. Woopah!