Short Summary:
- Load figure and clothing in Poser.
- Conform the clothing item to the figure ( Menu: Figure > Conform To... ).
- Select the clothing.
- Select Menu: Figure > Copy Morphs From...
- From the pop-up window, select only the morphs you need copied (you can usually ignore body parts you don't use, like head, hands, feet).
- The morphs associated with the body parts will then be available when working with the clothing.