We have another product PortraitPro Body which is designed for working on full body pictures.
Alternatively, in PortraitPro, when at the stage of moving sliders, scroll down to the skin area brushes and click on the "extend" button. Now you can draw over any area of the body where you see skin. The skin sliders affect all areas of skin including the ones you have selected. In addition, the picture controls effect the whole picture all of the time.