Well first you'll need a good modeling program if you want to do full body morphs easily. The morph brush is nice but for major work, you really need  to learn a modeling application like Zbrush, Scupltris, Blender or one of any others that allow you to edit the base OBJ file. Once you find the package that works for you, then you have to learn to edit the existing OBJ in the package of your choice and resave the morphed work back to a new OBJ that Poser can read. This is just the basic starting point.