Echoes, have you tried stretching your hamstrings to relieve periformis pain? I went to physical therapy for my back, and they gave me more exercises, but the most important was stretching my legs by lying on my back, raising one leg at a time, and gently holding the hamstring stretch (back of the thigh). I know it might seem counterintuitive because the periformis is in the lower back.

I used to hold each stretch for 20 seconds and repeat 4 times with each leg, and do that twice a day.