I did this successfully with a book I "borrowed" from my county library. The book appears when I first hit "My Library" and is not under "View my B&N Library" where my other books are. Hope this works for you.
I found in another answer that I
had to open the ADE first , then plug in the Nook, then drag and drop the book from the display on the black screen to the Nook icon under the bookshelves. Thanks