I definitely concur with the tennis ball treatment. This is fucking agony. My glute area is always riddled with trigger points. It burns at the time but you feel like you have a new set of hips when you're finished.
That external rotation (internally rotated) stretch is interesting. I've tried it and I have pretty poor internal rotation mobility. However I've never felt this limiting my training. Also, it feels like it puts significant torque on the knees, and I have to contract my internal rotators so hard to hold the position that I can't get a good stretch and I cramp up. Is it worth doing? I'll get the long-suffering girlfriend to help me if it is.