Here's what I did (I'm desperate to burn my SSWU and make sure I make the Elite 10K requirement next year). I have no idea if I'll manage the SSWU on the YVR - SYD segments since I'm not starting in Toronto on 033 but I'll sure try.

I cancelled the YYZ - LAX flight, and ate the $150 + tax fee against it (shame, was a $347 ticket after the discount).

Booked YYZ - LAX - YVR - SYD - YVR - YYZ. $400 less than YYZ - YVR - SYD - YVR- YYZ, plus a few thousand extra miles anyway (blows a day in a plane but I've heard of this "maximizing miles" strategy somewhere . . . .).

Couldn't use the promo code as it's not round trip (the LAX stuff screwed that up). Still was cheaper to do this way, plus the extra miles. The agent actually had problems booking because the promo code couldn't be reapplied. At least the credit was :-)