If you can manage to resolve his main proxy IP, and your BBS is written in Perl, Just place this line at the beginning of whatever subroutine makes posts
print "Piss Off" if ($ENV{'REMOTE_ADDR'} =~ /195\.167\.\d+\.\d+/);
substituting actual numbers for the hard numbers in the regex (195 and 167).
Something similar would also work for PHP.
Of course the "Piss Off" message can be changed to anything you like. lol
This avenue is much easier on server recources than .htaccess blocking or redirect.
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Bob
3x-x.com
Gallery Quest