Could the US offer statehood (or less drastic protections) to Taiwan? It would allow the US to have joint ownership claim over the South China Sea and enforce that for its allies - Japan, Korea, Vietnam, et al. It would also allow missile defense systems to be installed.

China would fiercely oppose it. But what could they realistically do other than start an invasion, which would be vehemently opposed by the world and be an end to their rise?

Offer Taiwan statehood.