x11 - ssh -X How to return a remote forwarded X application to localhost

I'm using Mac OS X 10.6.4
I'm opening an ssh session to a remote system running Ubuntu 10.0.4 Desktop

I open a remote VPN connection to a remote network
Then:
ssh -X user@host
screen -S openvas
sudo OpenVAS-Client #OpenVAS-Client GUI then forwards to my remote desktop

I want to configure and launch a scan in the OpenVAS GUI remotely over the ssh -X session. After I've launched the scan I want to send the OpenVAS-Client GUI back to its localhost, detach from my screen session, close the ssh session, and close the VPN connection. Hours later I want to be able to open the VPN connection again, ssh -X back into the remote computer, re-attach to the screen session, and bring the OpenVAS-Client back to my remote computer to look at the progress of the scan.

Is this possible?
Can someone point me in the direction of what commands and options to choose?

Thanks in advance.

Note: I don't really want to use VNC. I had installed NX and it worked in the lab but I can't log in over the VPN so that's a different problem.

Answer

Have a look at Xpra, it allows you to "detach" from and "reattach" to running X applications.