One of the biggest things that helped me with my stutter was to take jobs that forced me to interact and talk with people. It helped desensitize my own reactions to stuttering. In the end, I stutter less because there isn't as much anxiety and fear surrounding my speech anymore. And when I do stutter, I can manage it more easily. Most importantly your friend will be reinforcing the belief that he isn't held back by his speech. Definitely take the job!