To appease the powers that be, you could always just do HKG-MEL-PER-ADL-SYS and buy a cheap return ticket MEL-SYD. May cost you more than $100 of aggravation and phone calls to get someone to ticket it.

Incidentally, if you're going to be doing nothing but flying around Oz, you may consider doing a HKG-NRT turnaround instead and just losing the few hundred miles. Nothing against QF, but the experience will be nicer.