How hard is it to just stop responding to him? If he doesn't have your number, doesn't have your email, and doesn't know where you live, stop answering him. He has never been abusive to you, per your words, so just stop answering his IMs. If he sends 60+ a day block him, block every name he tries to talk to you with and just don't say anything. It's not that big a deal honestly.
If you can't do that then change your MSN screen name. It's not hard to do. You CAN, you just don't want to, there is a big difference. If it's really that big a deal change it.