Hi,
Well, i being working on a program that does exactly that, move and control AI traffic, you can tell it when and where to taxi, when to takeoff or land, and in which runway (and much more others instructions). Actually, i didn't published it, but i will when it will be finished. It is only for FSX, but you have the facility or option to connect all the traffic generated to a multiplayer session, so then your friends can fly with the AI traffic, and another person using the tower cab feature in FSX, can be ATC.
I know that in FSX there are some options to enable DEFAULT AI TRAFFIC to be visible in multiplayer, with this i refer that you can use FSHOST (or any similar multiplayer basic program, for FSX) and connect yourself to a session having the DEFAULT AI TRAFFIC in your FSX....TURNNED ON, (YOUR AI TRAFFIC DENSITY OPTIONS TO MORE THAN 0%). The main problem with this is that the AI itself CONFUSES ALL, AND INTERFERES with the players in the session, because you dont have control over the way that the DEFAULT AI TRAFFIC itself BEHAIVES, so there are moments where the AI lands in a wrong runway and also the DEFAULT AI TRAFFIC generated by your FSX is NOT VISIBLE TO OTHERS PLAYERS, and the AI generated by the others players FSXs ARE NOT VISIBLE to others NEITHER.
The only thing that my program requires is a person to operate it, which does the role similar to an ATC controller, but the difference is that the person is actually flying like 9 or even more AI planes at the same time.
Also, my program have the ability to create and move ground vehicles, not only AI aircrafts.
See my forum in my site:
http://www.fsmanuel.com/forum/viewthread.php?forum_id=2&thread_id=44
Best Regards,
Manuel Ambulo