I have absolutely no idea about the nerve block but wanted to throw this out here. I've been reading a lot about vagus nerve stimulation for migraines and other pain issues. Those done in the USA are through implants on the nerve. However, I came across an external VNS that's hand held called GammaCore. You may want to look into it. May be a dead end but you never know.

http://gammacore.com/en/healthcareproviders/

They use and have studied VNS for epilepsy, IBS, headaches, fibromyalgia. Seems like it probably will have a wider application in the future.