Change origination IP of a packet based on end point IP

I Need to change a network packet origination IP address if the destination IP is a particular address.

Here is my setup - i have a VM that is assigned three IP addresses, one data, one management and a third that is for external access.

The application works using the data IP address.

The application needs to make a call to a web service end point that resides outside the firewall.

The firewall only allows traffic out if the packet is originated from a specific IP address.

Using a test rig, I am able to send a packet out of the network using the external IP address the VM, so i know the firewall is working correctly.

Question restated - Is there a way to change the origination IP address in the packet if the destination IP address is a certain value?

If so, how would this be accomplished?

EDIT: These are Windows server boxes.