Your experience with punishment is pretty much like everyone elses - no matter how creatively you try to make the child suffer for poor behavior, it doesn't change behavior. Every aversive thing you've done to him hasn't made him buck up and behave.
And really, why should that be expected to work? Imagine if you were having trouble with a supervisor at work, and getting along with coworkers, and when you came home your husband tried to create mean things to do to you to make you do better at work. That wouldn't work any better than it does with kids. ;D That would make you, in fact, probably do worse.
I think you need to ask a broader question - how can we encourage him to do better in school, rather than what mean things can we think of to do to him when he continues not to improve.
You might go to the ADHD community on MedHelp here, and look for ideas there. Sandman, the community leader, is very experienced and can offer guidance.
Best of luck.