There is one drill, kinda hard to describe and I'm leaving to give a seminar soon so I wont have time to film the exercise. I'll try to describe it as well as I can.
First use a pronated grip (pull up... back of your hand toward you) harder to rely on the biceps that way.
From the pull-up hang position the drill consists of lifting and rolling your chest up without bending the elbows. Imagine bringing your chest to the ceiling while rotating back. Hold the top position and unwind back down.
You can either do reps with 3 sec hold at the top focusing on your lats or only doing one repetition holding the top position for as long as you can.
Then do pull-ups from that position: reach the "rolled up" position, pause for a second then finish the pull-up from there.
And eventually do the same thing but as once fluid movement.