You can do this with Poser alone, by exporting a morphed body part as a Wavefront .obj file, loading the second figure into Poser, selecting that body part, and selecting Add Morph Target from the Object menu.

Remember, morphs can only be exchanged between characters that share the same mesh (for instance, Victoria to Victoria, or Posette to Posette). Stephanie and Michael were built from the same mesh, so many of their morph targets can be exchanged.

However, it's easier to use a utility like Mason's Morph Manager 4.0, available in Free Stuff, to transfer morph targets directly from one character's CR2 file to another.