[Exim] Force local part to lower case?

I've got a system using Exim 4.10 and Cyrus IMAPD 2.1.6. I'm delivering
messages to Cyrus using LMTP over TCP/IP on the loopback address.

I just ran into a problem where a user tried to mail another local user,
but capitalized the local_part of the destination address. Exim routed
the message just fine, but Cyrus' LMTP daemon wouldn't accept it.

I have added another router to my configuration that does this:

lowercase_local:
driver = redirect
redirect_router = local_delivery
data = ${lc:${local_part}}

This is working fine, but I just want to make sure I didn't miss a
simpler solution...

Also, who is the proper person to email Exim "recipes" to for inclusion
into the FAQ? I've communicated with the documentation person for Cyrus
IMAPD, and gotten a (very) basic Exim 4 configuration included in the
Cyrus docs, but it would be much better to have a full-fledged
configuration sample posted. I'd be happy to forward mine :-)