I just did this. You can let Brad kill him almost all of the way (you might even be able to let Brad kill him all the way, not sure).
All I had was a bar and a sledge hammer when I started this. when you're running around in that big circle there is a sports store, I went in there and grabbed a hockey stick (right side wall) and started shooting those at him. It actually worked, Brad put the biggest dent in him but I finished him off. The same could probably be accomplished with the golf club.
Hope that helps.
If you NEED a gun look for security guard zombies (they usually have guns or night sticks) or go to the North Plaza, I think there is a gun store(not completely certain,look at the map).