Hi Scott F,
start with this stretch for the piriformis http://tatamihealth.co.uk/wp/our-services/piriformis-stretch/
The sciatic nerve can sometime actually travel through this muscle....typically those people that experience sciatic pain that don't have a significant disc bulge in the lumbar spine.
The stretch is similar to a glute stretch that a lot of people know, but it is a bit more specific this one.
Also keep up plenty of calf and hamstring stretches.
Aside from the stretching you need to improve your strength and activation in the gluteals in general. I'll try and post some more pics for you if I get a chance today!