another way is to reorder the verts.
- select the head and then the body, do a combine
- manually merge the connecting verts
- duplicate the entire character
- delete faces that were included in your original body, (excluding the head)
- center pivot and delete history on the new head (DO NOT FREEZE TRANSFORMATIONS)
you can delete history on your character as well
this has a way of reordering verts for you... so the blend shapes won't use the information from the entire body, only the head.
this allows you to bind the new head to a joint structure, create lattices, whatever method you use... and then duplicate the shapes off of the new head, apply all the blend shapes parrallel on the new head, and then use the new head as the sole front of chain blend shape input for your character.
Hope this makes sense