From Secrets of Figure Creation with Poser 5:

"Another item of note for the version section is a pz2 trick. If you set a pz2 file to version 3, you can use the code "on" and "off" for each body part to show/hide the part. In later versions, it is impossible to create a Pose file to turn parts invisible or visible."

Hide/Show pose files, example shoulder hide...

{

version 

             {

              number 3.0

              }

actor lShldr : 1

             {

              off

              }

Use .pz2 extension, just tested on v4, poser 8, works.