There's no Oneworld inter-island service in Hawaii; codeshares with non-OW airlines aren't allowed.

Getting to Maui on AA would require you to backtrack from the US mainland, which is against the rules. You'd also need to return to the mainland in order to connect to London as there's no Oneworld (or anybody's) service - yet - between Hawaii and Europe. And while JAL has flights to Honolulu and Kona from Tokyo, you'd have to rearrange your Asia segments so that you don't exceed the limit of four sectors in the continent. Remember when putting RTWs together you have to count every flight whether or not it's a connection or a stopover.

Have a look at his route instead - JNB-HKG-DPS-HKG-CTS-NRT-HNL,OGG-LAX-LHR-KEF-LHR-DOH-WDH-JNB. This would meet the criteria for a 4-continent RTW. You could fly on your own between Honolulu and Maui.