That's exactly my point. They have high ambitions and high expectations.
It would be possible to create the feeling that North Korea's behaviour and existence is a shame to them, since it's their backyard and they don't keep it calm.

This isn't about trade war mechanics or bargaining chips, but about the psychological needs and desires.
So far they can be amused by how easily the North Koreans fool the shallow-brained foreigners. Turn that perception into one of North Korea actually damaging the standing of China and being a chain that keeps China from being an example to the world and they might act very, very differently.

Turn North Korea into China's problem, period.
And I mean China, not just the Chinese government. Everything from caricatures and jokes up to political speeches in front of cameras and ruining days they intended to shine on.
Make them *want* to clean up the North Korean mess.