You've gotten a lot of good ideas. Hopefully you can find something that works for you.

As another suggestion:

Increase your outdoor time, if you can. He sounds like he has a lot of energy and I find outdoor time helps everyone (even me).

I had a 2 yo dcb who was at the point of not listening to me, my disciplining techniques were not working, and he was starting to get aggressive with the other kids. It got to the point that when he was doing something he was not supposed to, he got one warning, and if he continued on with the inappropriateness (eg: throwing toys, pushing kids) I put him at the table (I had one outside, too) with a few toys, books or colouring, and he had to stay there to play for a bit to calm down. I then told him he could try again. If it was his third visit to the table, he had to stay there until transition period (we had quite a few built in to our day). So not really a time out, but it gave him a break and opportunity to regroup before trying again, plus had the consequence built in of him not being able to participate if he couldn't follow the rules.

That is not an ideal situation,though, and was really my last straw with this particular child. I had been in contact with mom and let her know what was going on. It ended up with me terming him as he was singling out a child for his aggression and I was spending too much time dealing with his misbehaviours, however that is another story!

I think the fact that he is part time is probably having a huge effect on this, as well. I would pick a date on your calendar where you hope to see improvement, try some new stuff to see if you can get through to this kid, and reevaluate then.

Good luck!