Indeed. While Blondie is on the right track with a catastrophic WW1 defeat, I would agree with others that this would have so many other butterflies that WW2 would not happen in any similar way.
The Irish approach would be an interesting POD. Have Blondie's POD, then have someone in Australia attempt some sort of uprising (unlikely I know, but more so than IOTL), perhaps a left wing one in Queensland (?)? Then we could get a "stab in the back" issue going with both Britain/rest of Empire and internally.
Australia could be so messed up by that, even if pro British regimes remain or return to control, that the whole Pacific-Asia strategy of the post WW1 Empire is radically different.
I can actually give you that TL. It takes some odd decisions, but odder ones have happened. You basically need a POD where the UK decides India/Hong Kong is more important than the Aussies followed by hamfisted diplomatic skill worthy of Kaiser Willie.
1) Based on above, the UK decides to pull out the HMS Australia and HMS NZ. Not so sure on command structure on these ships, but lets say they were on the naval review in Portsmouth and don't go back. With fewer forces in area, Japan ends up with all the Germans lands in the Pacific.
2) See weakness, Graf Spee stays around the Aussies sinking ships for months before dying like OTL. A few Northern Aussie cities are bombarded. Butterflies but manageable.
3) IOTL, UK stripped shipping from China and other non-white colonies. Just have the UK decide to keep the trade with China going. After the war, the "evil business dukes" will be blamed. And it will be rich, connect business interests got the decision made. Severe shortages existing in Australia compared to luxuries in England and India. It may not be totally true, but has to be perceived this way. This is where you need PR blunders by English leaders to inflame the underlying perception. Quotes like "We will strip Australia bare if need to win the war" or "India is worth 10 Australia". Just dumb pointless things that make people made. Think GWB using the word "Crusade" in the last decade. Other words still rally the American public, and Crusade has big emotional meaning to Arabs. Same type of dumb stuff.
So after the war, the Aussies feel betrayed and drift away from the UK orbit. While they are anti-Nazi, they don't feel it is their war and don't want to fight over Poland again. Japan is happy with their southern border. The Aussies feel too weak to challenge alone, so seek some accomidation with Japan. When the Pacific war starts up, the Aussies act like Brazil. They sit on the sidelines until it is clear who is winning, and by the time the USA is winning, we don't want the Aussies help. ITTL, the Solomon Island have a network of bases built in the 1920's and 1930's, so it is not a soft spot. The USA uses the Central Pacific push as its only push.
This may be pushing plausibility, but with a few big blunders it could be doable.