You can't book a business saver from Hobart, as business savers are only available on Singapore Airlines Services. You would need a separate VA or QF booking (using cash, Velocity or Krisflyer points, or Qantas FF points) to get to MEL or SYD and take a Singapore Airlines service from there. From MEL or SYD, it is simple to tick the "redeem award flights" and then "add a stopover" buttons ,and select dates. NOTE: with savers online you can only add one stopover free of charge as a part of a return booking. If you want to add a stopover to a one way booking, or have two stopovers on a return booking, you need to call, it will cost you $100 USD extra, but if you ask, they still should offer the 15% discount as the functionality is not available online.