Avvo really deals mostly with U.S. law - and therefore in the immigration section, with "inbound" immigration: people migrating TO the U.S. rather than from the U.S. to some other country. I and most of my colleagues here (perhaps all of them) are U.S. immigration attorneys, and while experienced in U.S. immigration law we aren't really qualified to be giving advice about Australian immigration law.
I suggest searching the internet generally for Australian immigration lawyers, and ask them for advice about your situation before doing anything.
I would be careful here - for whatever this might be worth, what you suggest couldn't be done the other way around. In other words, it wouldn't be legal for someone to come to the U.S. on a visitor visa when their intent was really to marry a U.S. citizen and stay. I have no idea if Australia works the same way or not, but if it were me this would definitely make me want to check first to make sure I don't violate Australian immigration law and cause problems for a permanent visa application.