With pre-publication sales, consider offering, in addition to the pre-publication payment discount, something special about those paid books.  It could be author signed, numbered, include a color photo page, color divider pages, custom frontice piece, or an improved binding for an extra charge.  If the publishing project is for softbound books, offer a hardbound collectors edition price in addition to the regular discount softbound edition.  If going the hardbound/softbound marketing route, don’t forget to market to your libraries, especially if you are able to offer the hardbound edition for not much more than the standard retail for the softbound edition will be.