How about having biome specific blocks. These blocks could spawn particular mobs.
Like grass from a grassly land biome can spawn sheep if you place enough blocks in a certain light condition.
Stone blocks placed (Lets say 150+ of them) in light conditions 50% or less can spawn underground creatures.
This idea is borrowed from Creativerse as you can create dungeons or mob spawners for farming. But it only is for basic materials and such. Killing directly is faster and more efficient.