Well, what I was thinking was to use the exact same logic as the aim bot, and set up a potential aim bot for each client, but without actually making them aim. After that, you can check the average distance between where the script is aiming, and where the player is aiming.
If it's very small, and does not go outside the a certain limit, I would add a mark to that person's client. Too many marks means that the player is most likely aim botting.
A server pref for tolerance would be nice.
If I really wanted to, I could create a really complex algorithm to check if the player is botting, but again, I haven't the time. :/