Help configuring FVS336Gv2

OK. I believe I've got the hand of setting up the Multi-NAT. I create an inbound rule for each of my public IP addresses that points that traffic to the internal IP address of the corresponding server. This will allow those servers to actually be behind the firewall. And as an added benefit, those servers can now have a single IP interface on the internal network as opposed to having both an internal interface and an external (public) interface.

Now for my next question... I forgot/neglected to say that one of those servers has an application on it where it is making secure outgoing web services calls to one of my clients. That client has programmed into their firewall, the public IP address of my server. So am I able to also create an "outbound" rule such that if that server performs the call through the local IP address to the FVS336, that the FVS336 send it out over the WAN using the server's previous public IP address instead of the public IP that I've programmed on the FVS336's WAN1 interface?