I've built engines from scratch. I don't think that would work at all. It's a whole extra challenge to make an engine feel like a human. The engine has to come up with its best move and then sometimes choose not to play it and play something else for some reason. There are statistical patterns to how humans make mistakes based on their level, what kinds of mistake, how big and how often. Cheat detection is less about knowing the engine and more about statistics.

Maybe a pure neural net (no tree search at all) would stand a better chance. Shockingly, those can play at IM level.