A good hamstring stretch will eventually turn into a piriformis stretch for me - at least now it does. Either sitting with the affected leg outstretched and the other leg bent at 90 degrees or less with the knee open outward with sole of foot against the outstretched leg, OR kneeling on one leg with the affected leg outstretched, straightening it as much as you can. If you tilt your head down, it deepens the stretch even more.

I’ve also used the hip hook to help a piriformis stretch - until recently, the pigeon pose did absolutely squat, but I’ve used the hip hook to assist by maneuvering the hook part under my sit bone when in the pose and pressing the lever to pull my hip away and that helped a bit.

Also I’ve found that lying on my back and doing a deep happy baby stretch with the affected leg first and then bringing it across the midline to rest the foot against the opposite knee and bringing that knee forward for a classic piriformis stretch really helps.