Yes - you'll need to sideload them. How I got mine on there....
Download Adobe Digital Editions. Open it on your computer. Purchase the 3 books. Once they're purchased, click "open" which will open them onto the Adobe Digital Editions. Click the upper left button to make it look like a library again and not a giant book. Plug your Nook into your computer. Once it is listed on the left side of ADE, you can click on a book on the right and drag it to your Nook. Poof! Like magic it's on there. Remember to go to "My Computer" and right click on the Nook and go down to eject it before unplugging it.
This is also how you can get library books onto your Nook. Anytime you purchase any book that is available in different formats, purchase an ePub book for your Nook.