I also don't think this is really a challenge, because he wants Y. The challenge is getting seats in J or F to SYD. Since I'm bored, I just found 2 QF nonstop awards 12/27 on my first guess. More options through MEL. I didn't bother looking for Tahiti Nui, Air Pacific, or CX.

pacific - I can't answer your original question since I can only speak for QF. However, you're permitted a stopover in your gateway city, so you can visit both SYD and CNS (which is what I did on my award to CNS). Check this link: http://www.flyertalk.com/forum/showthread.php?t=440733