Piriformis Syndrome is a controversial diagnosis...
For one thing: there are several other diagnoses that could contribute similar symptoms. Plus, there are several theories as to what actually causes Piriformis Syndrome in the first place.
This is where it is so crucial that we, as clinicians, treat each patient individually.
It's possible that not every patient needs a Piriformis stretch. If the patient has a stiff Piriformis, sure a stretch is appropriate. But if movement patterns are faulty and glutes are weak maybe maybe those need addressing.
Here's an article that will educate your patients on what Piriformis Syndrome is, making sense of the different theories, and offering some exercises that address common impairments.