He wants an AI bot that doesn't fight against the player but against the player's enemies. A friendly bot.


Well, I'm not really good at ally AI but I think you have to code an AI bot (look up the several tutorials in the AUM or somewhere else). Then, where you tell him to attack the player, just tell him to attack all entities who are not in his team. A little more detailed:
You have just one action, for both the ally and the enemy. In this ation, you have a decision making function. Normally, somewhere in this function you say "if player is in sight, attack him". Now you say him "if entity with skill x != my skill x in sight, attack it".
So you have a skill defined that stores the team and that you set to different values.
It's very hard to explain this in english, it's not my first language.
Maybe some of the more experienced coders that are good at AI coding can explain it better. (I'd know some but I don't want to push them ;))