TAB Sportsbet have a bet called a tribet. With that, you can bet on each side to win by over 15.5 points or you can bet on either side under 15.5 points. Here is the betting on the Adel/Frem game:

FREMANTLE OVER 15.5 Pts $2.25
ADELAIDE OVER 15.5 Pts $2.75
EITHER TEAM UNDER 15.5 Pts $3.15