Somebody probably presented this years ago, but if not:
Sea lanes past the last base on the map would have a row of impenetrable (and indestructible) mines that would sink any ship on contact. Don't know about driving CV groups, but waypoints off the map should be disabled. This way, CV groups could be kept out of the fight but not so far as making them inaccessible to attack.
EDIT: An even easier solution would to disable the waypoints in place of the mine fields. The mine fields add a touch of realism, though and blowing up an entire CV group in mere seconds would look nicer than just having it bounce off an invisible line.
