I used to studder when I was about 6 years old (or was that just the stress of being the flunky in a dysfunctional family?). Anyway, I think most stuttering is from intense concentration and being overconcerned (self-conscious) about your opinions being accepted by EVERYONE (opposite of being opiniated), in other words, always worrying about being politically correct and that shallow people will criticize.
A more well humored attitude and arrogant confidence should help a lot. More relaxation with music and comedy shows or nightclubs should train the nerves and mind to relax and look at life and others differently. Realizing that life and people are not all they are cracked up to be (realizing that they're kind of shallow,...with all of their non-sensical and silly idiosyncracies) and seeing the irony of life should give him alot more confidence.