If you're familiar with the controls for call of duty, this would mean their right thumb was holding down the B button AND moving the right thumb stick while firing.
I'm sure there's some kind of finger yoga you can do to accomplish this, but that's hard and probably leads to arthritis. :)
It'd be MUCH better if there was an additional button on the back of the controller where your middle or ring fingers hang out doing nothing to improve your game while the rest of your fingers are hard at work.
This instructable is generic, and is also good for Battlefield players who want to press BACK to spot without moving your fingers.
NOTE: You WILL need to solder for this mod!
Step 1: Open your controller
To do this the right way, you'll need a torx t-8 security screwdriver. Or you can jam a micro flat head in on the side of the security nub and unscrew it until the security nub breaks off (like all of mine did) and then use a regular T-8 torx screwdriver.
Make sure you get the one in the middle under the battery pack and behind the sticker.