Run the service via Singapore instead of non stop. Then there is a wide body on that route to compete with SQ and Scoot. Onward passengers can be picked up in Singapore from the J* network and other Australian cities served by QF. Tickets could even be sold to passengers originating in Singapore.
The aircraft could easily be filled up as seats would be sold in different markets enabling selective discounting. Bali to London could be priced lower than Brisbane to London if required. A Singapore stopover could be offered as an alternative to Dubai or even an addition as both cities could be visited as part of a London trip.