Shoulder internal rotation using a ball and a wall with squat - Hand behind back

Stand with your back to a wall.
Place a ball, between your lower forearm and the wall with your palm facing towards the wall.
Apply gentle pressure to the ball and roll it up the wall as far as comfortable behind your back.
Try not to move your upper arm as you do this.
To increase the stretch squat down slightly once your arm is raised behind your back.
Return to the start position, and repeat.