If we're eyeing the expressways then, it might be possible to just try the tactic mentioned by euphonius on the (formerly) A9 highway that parallels the 318. Not sure what it's called now, maybe G60.

The idea then would be to get on the elevated road first which doesn't have a toll booth, and ride right through the first main toll gate on the right, just just after the elevated road portion ends and the official expressway begins --- somewhere around the Xu Jing area. Early in the morning would be the best time. Any takers on this mission?

Similarly, if anyone could post locations where it's easier to enter the expressway network in Shanghai than others, this might be worth a go.