The simplest way to do body parts is to :-

1. Remove everything from (a copy of) the OBJ but the required part(s).
2. Edit (a copy of) the CR2 to refer to the new OBJ and just the body part(s) you're keeping.
   N.B. If you want morphs to still work, you need to use a modelling program that doesn't reorder vertices (selective exporting from Poser itself is good enough).
   Some body part boundaries aren't very convenient, so be prepared to make transmaps to achieve full control of the cut and/or make morphs to tidy up the edge.

You can keep the morphs by turning off "Use external binary morph targets", so that they get written to the CR2 when you save to the figure library.