I'm guessing by the stony silence this question has accumulated, this isn't something that pfsense is going to help me with.
In the meantime, I came up with an alternate solution. I setup a vpn connection to my internal server using OpenVPN. I created a new interface with the external host's IP. I setup a route for that IP from my workstation across the vpn.
So, whenever I need to take over the external site's IP, I activate the vpn connection.
I supposed using a proxy server on the pfsense box would be a way to go to keep the solution on the firewall box.
Jim