You can make it so that a single team does not win by owning all cp's for attack/defend map play styles but i am not sure about both teams.
It's done in the team_control_point_master, take a look at control_point_round as well that might be of interest to you.
But what i can only think of is having a hidden cp below your map or something which is hidden off the hud (controlled in the flags menu of the team_control_point). So that not all the cp's can ever be capped. It's a bit make shift but it may well do the trick.