Would a feelings diary help at all?
We had a similar problem with my ds1 (also AS) when he was about the same age, although he was different from your ds, as he was unable to see the positive in any given day. He is in MS and was dreadfully bullied, but his bullies were far to canny to get caught. 
Initially, I created a very simple diary for him using very basic emoticons (happy face, sad face, straight/normal face). His teacher took 5 minutes at the end of each day to sit with him and get him to circle the emoticon that best explained how he felt about the day. To start with that was all we got, but eventually she started being able to ask him a bit about the reasons why he identified with that emoticon.
The next stage was when the EPs got involved and got him to scale his emotions. This involved laying a piece of string on the floor and blu-tacking some numbers 0-10 from one end to the other. 0 was the absolute worst feeling in the world, 10 was super happy. They then talked about things that made him happy, sad or just feel normal and he stood on the appropriate number along the piece of string to identify how happy/sad etc each thing made him. So, playing on his DSi was a 10, being bullied in the playground was a 0.
At the same time we worked on expanding his emotive language skills by teaching him new words to express happiness and sadness etc. So for example, ecstatic for super-happy, devastated for really upset etc. This was really important, because all he used to say was 'the worst ever' or 'OK'.
Then we redesigned the diary to incorporate the numbers/scale and new words, with them all set out along a scale on the front page for easy reference. We also changed it to be completed three times a day - after morning play, after lunch and at hometime and to include plenty of space for a sentence or so about why he had scaled his emotions as he had.
After a few weeks of this, we (and he) found that he was able to identify that no day was either all bad or all good and he started to gain some perspective. It also became apparent that it was an invaluable source of information for both his teachers and ourselves about what was actually happening in his day when the teachers weren't watching and this ultimately led to his bullies finally being dealt with once and for all.
It took a over year to get the system working right, expand his vocabulary and understanding etc, but its a great system that works really well now. This year I have added a parent/teacher communications page to the back of each sheet and that's been a really valuable addition as well.