AI Question in left 4 dead?

I was wondering if there is a way to have survivor bots not follow you as they do in versus gameplay. To see what im talking about load a versus map and set the game mode to versus (map l4d_vs_(map) mp_gamemode versus). Youll notice that the survivors will move along TOGETHER instead of following you. I wanna know if there is a way to make them do that in single player. Another is if ne1 has found out how to make AI spawn as infected in versus? It would be useful to fill in slots of left players on the versus side, and also it would b fun to play with them in single player. Any info would be much obliged!