Realistically I think the best thing they could do would be to work on it so that the zombies are really quite seriously formidable opponents... As in if you meet a group of them on your own you are in big trouble, and cannot get away from them without some pretty serious efforts...
yea in one video rocket said he removed the starting guns to see if it would make people group up at the start but all he really needs to do is make is so the cities are infested with zombie hoards and make it really difficult to explore built up areas.
do the same at the airport etc but not so bad in the small country villages