Selective banning/blocking

[Daniel Garcia <dgarcia @ hollyfeld . org>]

Unfortunately, I have a problem user on one of my lists.  I would like
to keep the subscription policy auto+confirm, as well as not have to
moderate the list.  Is there a way that I can block a single user/group
of users from being able to subscribe/post to the list without 
moderating the list or having to approve all subscribe requests?

Thanks in advance for any advice,

Cheers,

--Dg