Simple answer: No.

More complete answer: Think of the mmw as being like light. You can wear underwear made of one layer of Glad wrap, or underwear made of opaque fabric. There isn't any material that will protect your modesty but not be visible to the casual observer.

Similarly with the WBI: There are fabrics that millimeter wave energy will go through and let the TSA screener in the back room see everything. There are fabrics or materials that will reflect the mmw energy and show up as a bright spot, ensuring that you'll get the intimate patdown that the nude-o-scope was meant to replace. (There are fabrics that are in between, but they are either transparent enough to be useless or opaque enough to be suspicious.)