I read a life changing article in the Stanford alumni mag. about how to succeed in life it is more important to be someone who enjoys tackling a challenge than in having natural talent. She urged parents to compliment their children (and others) with phrases like, "You really worked hard to figure out that problem." Instead of "That is a great picture," say "I like how you used water color and all of the page."
William Bennett's book "A Child's Book of Virtues" is great to read from. Try to talk about people you admire from a character/value/becoming base rather than from an achievement/talent base. It sounds like he has been trained for several years in one way of looking at himself, so it will take time to change course.
I was top of my class for a very long time - it helped me to be around people even smarter than me to realize that no matter how hard I tried, I was not going to be the best at most things - even the smartest. So, as a kid, it would be good for him to have to be involved (and stick with it to the end of the course/season) in things where he is not the best.
Going together to help others - to learn to see that ugly/smelly/uneducated people have a lot of gifts and talents as well - is really rewarding, too. It is okay if you and he are uncomfortable to start off with - that is a great life lesson, too.
Don't try to do it all at once. Baby steps.