I think you're on the right track with your approach at home. That is, at any sign of aggression he should be placed immediately in time out. Then, when he re-joins the ongoing activity, he should not be with other children for a while (e.g., 15-20 minutes). Obviously he requires very close supervision, and to some extent vigilance will help. H eis displaying some immaturity in impulse control, but this will likely improve as strict limits are set and enforced.
The old days answer would be to pinch him back. I would really be tempted.
But of course adults are trained to REASON it out today.
Pinching makes a person cry and feel bad. He doesn't understand 'reason' in this case.
He just found a way that suits him as everyone jumps to attention and comes running. He has no idea it hurts.
Hopefully a CHILD VICTIM will do this back to him on his own, sorry for the crude answer.
Until then, time outs are great and effective. The other way would be immediate.