an option to disable auto-aim on controller

I play this on an xbox 360 controller. The auto-aim that's automatically enabled when using controllers really bothers me, and it doesn't make much sense. Say I'm looking at a teammate, 12 o'clock, he's surrounded by clots and getting torn apart, and there is a single spider-zombie, whatever they're called, at 2 o'clock. The spider zombie thing is less of a threat and there is only one. I aim for those attacking my teammate, to free him, and my sights automatically snap to the ground to the right of me, to the single zombie. I'm armed with a hunting shotgun. Will need both shots to clear out the zombies by my friend, can't afford to waste one on this tiny trash zombie. So while aiming, I try to pull away from it, aim for the zombies surrounding my friend again, and the second I line up the shot, my sights automatically pull back to the trashzombie at my feet on their own. I have to waste a shot. It's very frustrating.

Found a forum online describing how to disable it in the ini files, but I feel there really should be an option for this in the in-game menu somewhere.

an option to disable auto-aim on controller