I have done it. I have done one layer of Hobbs Poly down with one layer of bamboo batting. But bamboo could easily be substituted with W&N. It does add some extra weight to the quilt and it will be really, really warm. Too warm to use in a hot climate or in the summer in a cold climate. Here is a link to pictures of the quilt I did this way. It is heavily quilted though so the in process pics show a better "poof" factor.
http://www.quiltingboard.com/picture...e-t184706.html
Also Green Fairy does a lot of quilts with two layers of batting:
http://greenfairyquilts.blogspot.com/
Put your cotton on first then layer your poly on top.