Easier to just set a global ban on the nick rather than banning all the different addresses...
/ban nick!*@*
Or, if ident is the same, but nick might change:
/ban *!*ident@*
Just make sure you don't ban him while he is in the channel. If he sees what the ban looks like, he can easily know how to bypass it. Usually people don't think to change their idents if they don't know the ban is on their ident, for example.