So, sadly, there is no way to run this command with a command-line-only interface :(
Tom, if you read the link I posted carefully, you will see that it is entirely possible to use this command with a command-line-only interface. However, do you need an X server running.
You do not need a screen, you do not need a desktop environment, and you do not need the Mathematica GUI shown in a windows. However, you do need an X server. There are command line programs which render images which cannot be run without an X server. The purpose of Xvfb is to let these programs access an X server without a screen (and without graphical user-interaction).
