Sendmail LUSER_RELAY w/Cyrus: Default mailbox?

[Jay Levitt]

Using Cyrus 2.1.12 and sendmail 8.12.6, I would like mail for all unknown
users to be delivered to a specific mailbox.  I've tried setting
LUSER_RELAY, but since sendmail hands off all local mail to Cyrus, the
LUSER_RELAY is ignored.  I do have confLOCAL_MAILER defined as cyrusv2.

I found a very old message here suggesting a trick with rulesets and a text
file containing a list of all IMAP users.  I also found a patch from Carsten
Hoeger this past August (which was never incorporated into the main sources)
that adds an lmtp_luser_relay option to imapd.conf.  Are these still the
only way, or is there a more correct way to do this?  If not, any chance
that this patch could be incorporated into Cyrus?