Try to reprimand him as best you can without hitting the little aggressive guy, with a stern NO or some other signal. Some dogs HATE coins rattling in a jar or other clanging sounds like bells, so perhaps use that when he gets out of control.
Also, you can play with him, and then offer him a treat (some small piece of meat or something) when he DOES give up his toy. Then he can associate a good reward when he does do good things.
