Yes, you can! (Unless you are using our Upload writing mode - sorry about that!). If you are using one of the Leanpub workflows to generate your ebook files, go to the 'Export' page for your book and click on the 'Print-Ready PDF' tab, you will have the option to activate this feature. It includes things like alternating page numbers (if you're holding a print book open, the page numbers are above your thumbs) and alternating gutters (the space on the inside edge of each page in a print book, next to the book's spine). You can also choose many of the precise page sizes used by sites like Lulu and Amazon for the different sizes of books they produce.