Nigel, you might want to look into 1) cold laser therapy and 2) platelet rich plasma therapy.

1) Cold laser therapy is usually done by chiropractors and most insurances won't pay for it. There are two classes of lasers that are used for cold laser III and IV. Class III work well for not so deep muscle pain and if you have heat sensivity. Class IV goes deeper into the tissue and if you have heat sensitivity you might not be able to use it. There is some recent literature discussing the use of cold laser therapy on tendon and they show some good improvement in pain and function. It can go deeper than ultrasound for treatments. I have been doing cold laser therapy, both III and IV, for about 2 years and it helps with all my trigger points. I have tendinopathy of the adductors but my legs are too heat sensitive to use the class IV laser to work on the tendon and the class III doesn't seem to do much for the tendon. At least on me.

2) Platelet rich plasma has been used with some controversial success in patients with tendinopathy. Most insurance companies won't pay for platelet rich plasma yet as the data on its use is mixed but it might be something to consider.

You should be able to Google both of the terms for additional information for treatment but wanted to give you some suggestions to look at to help with you hamstring. Good luck and you are in my thoughts and prayers.