This is great of you to help him achieve something that will potentially help him the rest of his life. Just have him tell the interviewers he is shy, but his work ethic more than makes up for it, they are just a hoop he needs to jump through to get to the place he wants to get to. They are humans, put their pants on one leg at a time just like you and I. One time I was called about a guy that had helped me in the past, I told them they would be missing the boat if they didn't hire him.