[Exim] Route IP Range to a different mailserver

Using a router like this -:

#
       aol_route:
         driver = manualroute
         domains = aol.com:aol.com.au
         transport = remote_smtp
         route_list = * mailserverone.mydomain.com
#
    I can reroute messages destined for aol.com or aol.com.au to
mailserverone.mydomain.com

    Now I'd like to reroute messages destined for a specific list of IP
ranges to mailserverone.mydomain.com

    Say for instance, I might want to reroute all messages bound for
192.168.10.0 and 10.0.0.0 to mailserverone.mydomain.com

    I've looked all over the place, and the only idea I've come up with a
clumsy hack using the ignore_target_hosts option in the dnslookup router....
Is there a way to do this simply and correctly??

Thanks in advance, for any suggestions!

---James :) Collins