AFAIK, Poser has no elegant ways to do this. You can indeed take a secons Jessi and conform her to the first, but I found this slows down rendering dramatically since Poser has to find out for every facet which of the two geometries is visible. It may help to add a small displacement value to the 'cloth' figure. By all means clip off any limbs you do not use, or at least set them invisible. Do not rely on transparency only. Real 'layered textures' apparently are not supported by Poser.