You know what, it is possible. But i see it as WHAT subjects you do, as opposed to HOW MANY you have in Year 12.
Sure, have completed 7 3/4 subjects does help in some way, but it also depends on whether the subjects you are doing will be affected by good or bad scaling.
In year 12, I like to think I studied my ass off. There wasnt a time where you wouldnt see me studying. I studied before, during and after school, as well as weekends, skipped social events to do homework, took time off work nearing exams and aimed for at least 7 hours a day. And you know what? i didnt even get an 'awesome score' as you may say. Actually i got a pretty shit score, missed out on getting into my 1st,2nd or 3rd preffernces and didnt get an offer 1st round.
However I just went the wrong way about it. Having said that, the dux at my school did have a life, went to parties, had a boyfriend, got her p's, etc, did reasonable amounts of study, and still scored in the 90's. But she did science/maths subjects, whereas i did mainly humanities/arts (which scaled down)
So long story short. It depends on the subjects you actually do

Good luck and stay strong.