Stacking with zerg is easy, stack some protoss/terran buildings (alot of them) and kill one, build a creep producing building (hatchery or creep colony) and then wait for the creep to spread under the building. When it is done, you can just build there (even with lights on). Then after building under it and you want to (and can't) build more, kill another of the terran/protoss building. It's a little more complicated, but it works.