There's no way to get rid of a pretender, that I know of, once they've been uploaded. These games that Zach hosts aren't terribly well organized, and this has happened every one of them I've been in. Invariably the person will stale for several turns since nobody is playing him, and he'll either be overrun, or set to AI.
edit: oh Tibbs, can you give your password for eriu to a friend so he can just log in and set it to AI? that way we won't have to wait till the end of each hosting period... And if you log in, anti-cheat will get you i think