I moved my linux box to my basement, and I don't have a monitor attached to it any more (previously it was hooked to my 1080p tv and displaying 1920x1080)

I am only accessing this machine through remote desktop from one of the laptops.
Since the move, the max resolution is set to 640x480.

Is there a way to change this without having a display attached ?

I would very much like to avoid tweaking xorg.conf as I do not have a monitor available and still need the box to boot and run ubuntu. Having it not boot would be VERY unpleasant at his moment.

Thanks in advance,
RMcB