[exim] Logging message deliveries to hosts

I have a number of satellite hosts that I deliver mail to, and I'd like
to log message deliveries to them in a MySQL database table. The router
and transport I use are

boxes:
driver = manualroute
domains = *.boxes.retail-sc.com
transport = remote_smtp587
route_data = ${lookup{$domain}lsearch{/etc/mail/boxroutes.txt}}


remote_smtp587:
driver = smtp
hosts_require_auth = $host
hosts_require_tls = $host
port = 587

I'd like to have the recipients_count, message_size and the target
host ($host), but I cannot think of a ${lookup incantation anywhere
that would solve my problem.

Any ideas?
    -JP