Unfortunately, the rates are per country, you cannot book a flight on another website than US with a departure from US. You can check a return flight from HK to SYD is half than return flight from SYD to HK.
Sorry, I was probably a little vague. I can price the flights I want and get all the way to the payment page, but I am a little concerned by the FAQs which seem to be suggesting that the flight may be "repriced" if my card is from a different country. I just don't want to hit pay on one price, only to have them recalculate based on my country of card issue and not the country I wish to ticket from.