Mathematica: Resuming SSH evaluation with XMing

I am re-asking this question since it exactly applies to my situation and it had received no answers earlier:

I currently run my Mathematica on a linux computer through Putty and Xming. Xming provides a graphical display for Mathematica windows ruing on a remote linux computer.

But recently, the network has become quite unstable. A disadvantage of using Xming is the graphical display will disappear immediately as soon as the network goes down. When the graphical display disappears, all the evaluation that is ruing stops and is lost.

So I wonder if there is a way to control to make notebook cell evaluations run in the background when I use the graphical display to run Mathematica remotely. I expect that code ruing in the background will not be affected by the shutdown of the graphical display.

I am aware of the answer suggested earlier, namely using screen. However, how do I open the Mathematica GUI (the notebook already being evaluated) after reattaching? On simply typing Mathematica at the command prompt, it just opens a new window altogether!

Thanks for all your help.