I've been wondering about adding "outside" flavors and aromas myself, and how to get them into the beer, effectively. There must be some great wisdom and research on this board and other places.
As with all aromatic things, you want to extract the oils that contain or carry the flavor and aroma. Then once extracted, you don't want the boil or fermentation process to strip them out, or convert them to other, not so desirable components.
For example, adding cocoa powder to a primary or secondary will yield very little or no chocolate flavor. I guess same things happen with your PB2.
I read this article on a dry hopping method where the beer is being circulated (pumped) through the hops for 24-48 hours. Now that is a good method, that beats the "add pellets and let sit for a week" approach.
So, find out how to get those specific essential oils into your beer and you're (half way) there.