Accoding to the descriptions the skirt is conforming clothing which includes several morphs and dial movements.  Unless there are specific dials that control skirt sitting positions, you will need to resort to other methods.  Poser's morph tool might help move the mesh to a desired pose, magnets might also do the same.  However, the best bet would be to convert the skirt to a dynamic piece of clothing for better draping.  But the pleats could present a problem as well as the embedded safety pins.