Cant you just set it when you're starting your server?
Go "New Multiplayer Game, and there should be a bot difficulty setting selection right there. Does that not work?
Also, go to the CPU Player Options tab at the right. There should be "Limit CPU players to " then a drop down box or something, and you should be able to set them to one team.
or use bot_add_ct/t (its what I use withnout AMX) and take off team autobalance.. just add bots to the other team when more people join.