I had pec minor problems on my left side. The one and only thing I ever found that fixed them was this exact stretch, but done with a heavier weight (such as a buckwheat pillow or a book):

http://www.youtube.com/watch?v=oAY2OWGKLe8

You might start with 30 seconds each side. Do 1 - 3 cycles. 2 X per day.

Now that my pec minor isn't so tight, I do 1 cycle of 30 seconds each side, 2 X per day (morning and late evening).

I'm extremely happy with the results. I used to get severe pinching and circulatory effects.

There are some other pec minor stretches, but I had problems with them. For example, in one you are standing with your arm raised. Well I have TOS and raising my arm cuts the blood flow off so that's a no go.

Some people like the stretch where you lay over a bolster or an inflated ball.

Have you already tried this stuff? If so, how many reps, duration, times per day, etc. did you do and for how long?

You could also look into ART, manual therapy, therapeutic massage, etc. but I would still try the stretch.

Good luck.