Route - Internal IP to External IP

Hi,

Is it possible to route traffic between an internal IP and an external IP that's not bound to the external interface?

We have a video conferencing system that we just cannot get to work through TMG, that allows 'screen presentation' from a PC, so the PC screen is embedded in the video stream.

If we put the video conferencing system directly on the public internet (with one of our public IPs) it works absolutely flawlessly.  However, because the internal PC is then on a different network to the video conferencing screen presentation now no longer works, because the 2 can't talk to each other.

http://i.imgur.com/7nAizG0.png

Thanks