[exim] lookup default

I have a transport like this:

LOCAL_DELIVERY_OSB:
driver = appendfile
mode = 0660
user = 1xxx
group = osb
mode_fail_narrower = false
envelope_to_add = true
return_path_add = true
use_fcntl_lock
file = ${lookup{$original_local_part}lsearch{/etc/exim4/osb_users}}

The osb_users file has entries like this:

dan       : /home/osb/Mail/dan
john      : /home/osb/Mail/john
sue       : /home/osb/Mail/sue
webmaster : /home/osb/Mail/sue

I'd like to make a default 'catchall' user and send that to dan. How would I do
that?

Thanks,
Rory

--
Rory Campbell-Lange
<rory@???>
<www.campbell-lange.net>