I don't think so. With this ability you can only specify a network where firewall will do NAT
or where will not do. I think you need transparent proxy. It's similar to port redirection in
inbound NAT,
but on LAN interface. You can't do this by m0n0wall webGUI, because it works only with WAN 
interface.

Petr

> With the ability to configure destination for advanced outbound NAT in
> m0n0wall pb19, can m0n0wall redirect all outgoing http requests to port 80
> from client machines on the LAN segment to a Squid proxy on listening on
> port 3128?
>