So first, alter server state before transmission by spawning hallucinations (human-like bots) in places not visible to human players (inside walls, unusual angles, far in the horizon). To the client, they all look like human players. At least in memory.

The players who react or interact with these hallucinations are likely cheating.

This flips the roles, and the hard task of correctly determining "human like" behaviour is now on the cheaters.