Remember when you were little and on a sunny day used a magnifying glass to harness the power of the sun to burn leaves? Well, this technique can be applied to psi spheres. It is important to already be familiar with the creation and manipulation of the psi sphere technique before attempting this modification.
Think of your palms as two magnifying glasses that concentrate your Internal Energy to a point exactly in the center between them. Visualize your energy being focused by your hands and flowing ever more densely as it approaches the center point between your palms. After awhile you will build up enough energy to allow the psi sphere to begin growing until it has filled the spherical region between your hands (like the flame grows to consume the dry leaf).