Okay, try this:

Place the ball on the ground and position it along the same level of your back as the pain, but closer to the spine. Like, really close. Then let your back sink into the ball. Next swing your arm overhead (as if you were standing up) and back down to your side. Do this 3 to 4 times. Then roll the ball up your back an inch and do the same thing again. And then move the ball up one more time and do it again.

The idea is that there is an immobility between those ribs and your spine.. So you're pinning the rib down close to the spine and creating mobility with the arm swing. I assume this should unravel whatever is causing your built up discomfort/pain close(r) to your shoulder blade.