If you haven't purchased them yet I'd search some of the other ScentLok/activated carbon related threads on these forums before investing that kind of cash . You'll quickly find what a waste of money they are and why . They are a temporary solution at best , and a very expensive one .
Here we go
AGAIN. 
Let it go man. It's his money. Let him spend it like he wants. Just because you don't think it works, doesn't mean that it doesn't. Jeeeesh.
To answer your question, never put any kind of scent wafer or anything in the back with your suit. It can or will reduce the odor adsorbing capability of your suit.