I can check with the powers-that-be, but beyond banning the account there's not really much else we can do. Inactive accounts are deleted periodically (you have to be inactive for a fair amount of time, I believe,) so if you don't log into it, it'll just go away on it's own.
If you really want a ban on the other account we can do that, just PM a moderator with the details. I would say that's kind of unnecessary, though. If you're not logging in under that account or posting with it, then as far as anyone is concerned it's effectively the same thing anyway.