It's a no brainer. Go to the website and request a jump seat. Takes about 3 minutes to fill out the online form.

The hardest part would be to figure out where to meet the crew. Usually at their hotel or at base ops.

That being said, flying to Sydney, I would first look at using United or any other legacy that goes there, with Atlas as a backup. It's just way easier and much more frequent. Just don't get yourself listed and then not bother to show up. Atlas goes out of their way with catering and whatnot, and no-shows tend to irritate them.