I don't know anyone that could achieve fluency in English in three months, but what may help is if you familiarise the student with "Oz" (As many Australians call their country) I wouldn't worry too much about the spelling, he'll be speaking not writing. Concentrate on vocabulary and basic grammar, and teach him about Australias history and culture. He'll be meeting ordinary Aussies who won't be particularly bothered how good his grammar is. It's all about communicating, so concentrate on building his word power and confidence.
Find out where he's intending to travel in Oz and find it on this site
About Australia -The Australian Travel Guide
You may find inspiration here.