I am afraid the short answer is: You can not - at least not in SimulationXpress. You will need the full version.
However. From time to time I have some purely 2D issues. I have had success by making an extrusion an by varying the length of the extrusion (not the force/pressure) I can to some extent control the displayed scale of deflection.
It is not ideal but it is cheaper than the full Simulation package.