nnmail-split-methods question

[Bill White <billw@wolfram.com>]

Pterodactyl Gnus v0.97, GNU Emacs 20.4.90.1 (i586-pc-linux-gnu, X
toolkit) of Mon Nov 1 1999 on g.wolfram.com

(setq nnmail-split-methods
  '(("misc.typo" "^return-path:.*typo-l.*")
    [...]
    ("cf" "^reply-to:.*gabriel.ma.us.*")
    [...]))

How can I use nnmail-split-methods to split mail into monthly groups
named, for example, like "nnml:group.yyyy-mm"?

I have some nnml groups with over 10,000 messages. When I get new mail
for those groups, I'd like to split the messages into
"nnml:cf.1999-11" for messages received this month, rather than the
gigantic "nnml:cf".

Next month (December) I'd like all mail from that list to go to
"nnml:cf.1999-12".

Thanks -

bw
-- 
Bill White . billw@wolfram.com . http://members.wri.com/billw 
"The whole pleasure of marriage is that it is a perpetual crisis." 
-G. K. Chesterton, "David Copperfield," Chesterton on Dickens, 1911