Turning an AI unit to player control

[BIGBAD]

I have a 4 person MP mission with an intro. The intro camera zooms in on our 4 characters walking down a road. Now, once this small scene is finished, I want my 4 players to take control of these characters.
  I can't assign them as players from the start, obviously because the characters will just stand there during the intro (when they should be walking).
  I assume they have to be AI with a MOVE waypoint from the start, and then they somehow need to a script which allows them to be controlled by the players when intro is complete.
Any help on this greatly appreciated.

[Black_Feather]

You can't change control of units. But you can use dummy units, make 4 AI units like you said witha move waypoint and then when the intro is finished and the screen is black you can just setpos the players into the positions of the dummymen.

unitname setpos getpos dummyunitname