-wait in the bathroom upstairs and smash his head with an axe(shack in the park) when he turns his back on you
-get a shotgun (second house on the right), get out of the other door when he is waiting and shoot him
-maybe barricades? (crafting: hammer, boards and nails)
My experiences with him were different. Sometimes he just took of the barricades and shot me without a word (maybe a bug). Later he always waited at the door and did nothing.
One time a horde of zombies came and he shot them all - attracting double the amount of zombies that finally knocked my door down and killed me

You can play around a bit, but it's not really much of a game atm. But it will be
