Get aggro
Climb a ladder, up to top of e.g. hospital
Walk to the other side of the building
Zombies are following you through (or around) the house
Walk back and forth
Climb down at any side of building - zombies will be waiting downstairs no matter which side you choose

Run around through buildings, going left/right/up/down randomly, do this for like 5 minutes
Zombies will still be on your tail, impossible to shake them