In the long term I guess it's about teaching him to get himself out of situations that are likely to trigger an outburst before the outburst happens - my dh is still learning this one in his 30s.
I would guess the pp is accurate in that its not "him" when he does it, it's like an instant snap into another person? In which case there is less time to identify the feelings in himself. The strategies we are trying are very gradually building up the time between thought or feeling and action... But the problem is four year olds don't yet have the brain development to judge outcomes, they are emotionally driven, and asd kids even more so.
It's a really tricky one and as I said, dh is still working on it years later. Good luck!