After a bit of peeking through the exmh tcl and playing with tcl a bit, I got
the "catchup unseen messages before cur" procedure working.  Here's the code
for everybody and the list archives in case anyone wants it in the future.
Thanks to John R. LoVerso for putting me on the right track.
If you want to use this, stick it in your .tk/exmh directory, run auto_mkindex
on it and add the following lines to your .exmh/exmh-defaults:
*Fops.more.m.l_ketchup:         Catch-up all before current
Check Website or Keyserver for PGP/GPG Key BA0349D2         secabeen@pobox.com
"I have taken all knowledge to be my province." -F. Bacon  secabeen@cabeen.org
"Human kind cannot bear very much reality."-T.S.Eliot        cabeen@netcom.com

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In-reply-to Ted Cabeen <secabeen@pobox.com> message dated "Mon,
    30 Sep 2002 11:57:27 -0700."
From exmh-workers-admin@redhat.com  Mon Sep 30 21:44:31 2002