Do what I did with my green severum when he was being aggressive. Stick him in a different tank for a while then put him back. He's now the new kid at school in his mind.
Or possibly whenever you see him being a bully stick him in some kind of container but leave the container in the tank.
I put my severum in a kritter keeper but left it in the tank when he decided to be aggressive. He tried it 2 times then on the 3rd time he stayed in for a week and now he's mellow. I think not feeding during that time could either make his aggression worse or less.