With AA one-way stopover rules, you can stop in the North American gateway city (the city from which you leave or enter the NA region). In this case, the city is HNL. You should be able to search on the AA website using multi-city dates on the home-HNL segment and HNL-SYD segment and, if you choose the exact same type of award for both segments, it should price the same as just LAX-SYD.