Dear Steve,
Yes, EShop has the feature for you to do that. Please go to the back-end of your site, then go to EShop -> Sales -> Fields. Choose country_id field on the list to edit it, under General tab -> Default Values, enter 13 there and Save. (13 is ID of Australia country under EShop -> System -> Countries)
Then test again.
It should work as your expect.
Sincerely, Giang