Have a look at the schedules and see how they fit around these city pairs.

MEL-SIN QF/BA
SIN-BKK AY/QF codeshare
SIN-DPS QF

and then you could connect from either of the Asian ports above to HKG. So if the schedule fits, I am suggesting something like
MEL-SIN
SIN-BKK
BKK-HKG

or

MEL-SIN
SIN-DPS
DPS-HKG