If its the CircPac22K, then its not. Probably the closest you'll get to is DFW. In which case you can do SYD-AKL-LAX-DFW-YVR-HKG-SYD. Then use an AAward flight to get to CUN. This AAWard is just over the limit for 20K QF points (you'll need 30K), so you might be better off spending 20K points and going DFW-MEX-DFW. Easy, cheap and good busses to get anywhere in Mexico.
If you really want to go via SCL, you have to get the 29K CircPac ticket. Also, if it's in D (ie J class), you'll find a DONEx ticket suddenly becomes a good option - even if it starts in BKK and you add the award or normal fare to get there.
If by chance you want to go to HAV (why else go to CUN), have you considered the xONEx and go SYD-Europe-MAD-HAV-SCL-AKL-SYD?