After seeing many lots with slimes covering them (due to 1.4) because of their location in a swamp, why not just set the BiomeSet flag?
This flag changes the biome of the lot, much like World Edit's //setbiome! If your lot is in a area like a swamp or jungle that you don't want slimes or those bliddy cats spawning anywhere, you could just have a Mod+ change the biome. This feature would probably only Mod+ so you would have to put a request in, but I could see a SuperVip+ or a Goldy+ permission.
Well, that's all from me!
-luetzj