Sydney is a place of which I am none too fond, however from my experience, I have found that when towing and you indicate the intention to change lanes, the cars in the lane in which you intend to move, show courtesy and wait behind, sometimes even flashing their lights to let you know it is safe to move over.
Quite the opposite to a lot of the rude buggers in Melbourne who would happily push you off the road to make sure that they were in front. Sometimes it is a case of indicate early at your peril as they may very well speed up, bunch up, and block you in.
Maybe up your way they have an aversion to using indicators?