:iagree: The above method works best here too - finding activities that DS can struggle with and things in which there isn't always one "right" answer, i.e., drawing.
Also, pointing out mistakes that I make in his presence, reinforcing that EVERYONE is imperfect.
Finally, we got a lot of good ideas out of a book entitled "What to Do When Good Enough Isn't Good Enough - The Real Deal on Perfectionism", by Greenspon. It's aimed at kids (although we read through it together) and it was very eye-opening for my DS.
HTH!