I have not been through this, so take this idea with a grain of salt or two.

Has he ever been to a counselor? I wonder if you called a reputable practice and explained the situation (including his refusing to go see a counselor), if they would have advice for you. I am guessing that it is not unheard of for someone to not want to go...

As for talking to him about going, does he understand that his approach (anxiety driven) is going to continue to keep him from doing things he might otherwise absolutely love until he learns some new techniques for managing it (i.e. what the stranger knows and can help him know too)?