You can selectively add support to only certain areas of your model using support enforcers and blockers. For this example we will add an enforcer to the model on the left and a support blocker to the model on the right.

Right click on the model you wish to add a support blocker to, and select Add support blocker. Follow the same instructions for a support enforcer, but select Add support enforcer.

A 1"x1" cube, sphere, cylinder or slab will be generated based on your selection. The dimensions of this object can be modified by selecting it and using the scale tool from the lefthand tool bar, by selecting and dragging the square handles for each axis.