The physical store has limited space for books, so they only have the newest and most popular. BN needs to stock the self with paper leaflets of 2nd and 3rd tier books that could be bought in the online store. The leaflet could contain a QR code so shoppers could buy the book right then using their phone.
This would expose more people to the online ebook store and draw them into titles that BN can't stock physically. They could even give them a "free" first book to incentivize people into signing up. Educate the staff to help non-technical shoppers sign-up and get their book.
The overall experience would be to teach people how to use the nook app to buy books. Once people are comfortable with the process they will be apt to buy more books through the app.