This would be a nice add-on depending or how much the additional polys affect the render time. One post work trick to static renders is the set your pose then export your clothing object. Use the extrude in just about any modelling program to add the thickness you want. then importing and render. It's not perfect but works ok ( even easier if you have ZBrush and use goz). Sometimes a bit of post work is needed. BTW as I mentioned above this DOUBLES the poly count and can really slow rendering in some cases.