Instead of banning ips for a players client, mabey each play can have an assigned number, here is somewhat of an explaination of how it works, feel free to amend it.
On the site, the player logs in. It will take him to his account information page, and he must enter his password and stuff, and email. A number is assigned to that player and all his accounts. (I don't know any other way to id the player so he gets a number
)
When banning players, their id is banned on the server so they can't use another account to login.
Seems complicated to get a id to each player, but I don't know.