I had never heard of powdered PB but that sounds excellent since it is the oils that you need to remove since they inhibit yeast growth and tend to put off flavors with hops.
Remember, since you are removing the solids and the oils, you will need to use a good bit to get any PB flavor at all.
Let us know how it turns out!
Cheers,
knewshound
http://www.bellplantation.com/