There <are> a couple of ways to filter an obnoxious user without it
showing up in the list header.  But they involve the LISTSERV maintainer,
so list owners can't do this themselves, and they also involve cutting
the user off from <all> lists on the server.  If this person is that
obnoxious, perhaps you should contact your local maintainer and ask that
either this person be permanently served off, or added to the FILTER_ALSO
site configuration variable.  Naturally the response you will get depends
on how your LISTSERV maintainer feels about cutting users off from the
entire server.
 
Nathan