Here's what happened.

I got off the bus at the international terminal, and looking into the immigration area it looked like it would be a very long wait. This meant there were ideal conditions to test the Pier C trick.

Walked down to Pier C immigration and there was no wait at all. Immigration officer was halfway through processing me when he noticed the flight details. He said, "I think you'll find that your flight leaves from the other pier" and he started to hand my paperwork back to me. Rather than explaining that I was testing the system so that a bunch of frequent flyers could save time, I just said that I was meeting someone in the Singapore lounge. He said, "Oh, OK" and finished processing me.

So it can be done, but it seems they prefer you to use the "right" entry. Don't really see why they care - the airside transfer is quick and easy, and it's not as if you need to pass through extra security or anything that would take up more resources.

Can't be very common though. The women in the Duty Free shop were confused by the Qantas boarding pass, and one asked where QF 11 went.

I would certainly do it again if the Pier B immigration lines were long. Mind you, it was an odd experience being all alone in the middle of a hectic Sydney airport as I walked back along the corridor to Pier B - not another soul in sight.

P.S. Thanks for the op up Qantas. Those Skybeds are great.