2 Player Boosting Method:
Since whoever gets the last hit gets the achievement, this is much easier to do in VS Survival
with another player.
-Make a squad with your friend.
-Set the options to VS Survival, Normal difficulty, Short (4 waves), and set the match to Invite Only.
-The Human player fights off 4 waves while the Zed player runs to him to die.
-On the Boss wave, the Zed player becomes the Patriarch.
-The Human player shoots Patriarch player one or two times, and then Patriarch quits.
-Human player will unlock the achievement (along with the Human VS win, if you didn't have that already).
-Rinse and repeat for the other guy.
If anything isn't clear, feeling free to let me know in the comments.