I expect that the Dept of Immigration (passport control is not customs) will send someone to Bendigo, (or wherever) to check passports and collect departure cards (you will still need to certify that you are not taking cash, native animals, out of the country, etc). I also expect that you will be charged for the time & travel costs of the officer (s). There may also be some manifests required to be completed in Aust. that are then presented to the arrival country. If you have ever sat near the front door of an international flight you would notice that there is a fair bit of paper and bureaucracy that goes on before anyone can disembark. This will still be required for a private flight. I think some of the paperwork might be under government to government treaty, in which case it must be generated in Aust.