I go to a preventive MD who uses all sorts of natural therapies. I had an allergy test, a very comprehensive, expensive one. It is supposed to be the best. Who knows for sure, but I trust her judgement.
Anyway, I was allergic to 13 foods. Tomatoes, and red pepper were the only night shades that showed up.
After an Elimination Diet for a few months, she says you may rotate in the foods you were allergic to at one serving every 4 days.
For persistent allergies she also offers the Nambdripad desensitization technique. I have the books about it I bought years ago. One is called Say Goodbye to Illness by Dr. Devi S. Nambdripad.
It would depend on if it is true that nightshades are poisons for everyone or if it truely is just an allergy, but there isn't agreement in that area, so you could experiment.