You do have a few options;
Macquarie has a post grad medicine pathway, where you do a clinical sciences course for 2 or 3 years, of which the last year consists of GAMSAT preparation, so may better align with your intended pathway.
With regards to reserving medicine spots, ANU has a postgrad pathway, where you do a medical science degree for 2 years (in a cohort of 60) and then 30 students are selected for a 4 year post-graduate medicine degree (of which 10 seats are reserved for rural or Indigenous students; I'm not sure which out of the 2). But the disadvantage would be having to move out for 2 years.