When my daughter decides to throw a temper tantrum, she now knows that we don't want to be around her when she acts out like that. The tantrums (though it did take a long time for her to truely make the connection) have lessened and are fewer and farther between. Here is what we had to do.
Each time she started to throw a tantrum about something. She was completely removed from our sight, sent to her room and the gate was put up so she would not be able to come out until I said so, sometimes two gates are necessary to block the doorway. She knew that her time-out did not start until she had calmed herself down and that I wouldn't even talk or respond to her until she had calmed down. Thus removing the underlying reason for throwing the tantrum in the first place...attention. She lost it completely when she did what she thought woul get her more.... At first, it was EXTREMELY frustrating listening to her scream for an hour from her room (I had to step outside and call a friend or my sister-in-law to calm myself down) but she began to see that noone wanted her around when she acted that way.
Now, a year later, she knows that if she has a tantrum and we tell her to go to her room or stop (have a number you count to to show how much time he has to calm down). We count to 5 or down from 5. She is usually done with her tantrum by the time we get to the second or third number. There are times, too, since she no longer is required to take naps (became too much of a fight about a year ago), where I tell her that her morning behavior says that she is tired and she either needs to sit and read books in her room for half an hour or she can take a nap and I will wake her up with her brother. Often times her tantrums were brought on by sheer exhaustion.
Well, I hope this helps you. Just separating him from you and taking your attention completely away with unwanted behavior may not work with him, but if you decide to try it, be sure to give it a couple months, it is not a quick fix, there never is one with our kids.