I run a private server for my friends, and want to make a specific area mob-safe, without placing any block or light it. Changing the global difficulty or mob-spawning server property with command block is not an option: even if somebody is insed the area (enterieur of a huge building, actually), I need the mob spawning on the rest of the map work normally. Changing the biom to mushroom island is also not very good, because it is in the middle of a huge desert, and I want weather to work the same as its surroundings (ie. the rest of the desert).
Is there any way to do this, via command block, map edition, or maybe modding, scripting, etc.?