By signing up? They launched it there already. Disney+ launched in Australia, New Zealand and Puerto Rico on November 19, 2019, and is set to launch in the United Kingdom, France, Spain, Italy, Germany, Ireland and "a number of other countries in Western Europe" on March 31, 2020.
Oh, actually I wasn't aware it launched in OZ. I will be in Thailand when Togo releases next week, how can I watch it? VPN?
So if you are from Down Under, yes, you can sign up. But I am not sure what Disney's policy is about traveling with your account. Netflix doesn't give a shit, so I was able to watch it in Europe with my American account. (this is about licensing in different territories and not screwing the costumer) That doesn't mean Disney has the same policy. Technically a VPN should work, but practically Disney may block such sites. So you won't know it until you try it. They have 7 days trial so you can always just check out if it works.