From an observer and edited:
As you astutely observe, the North Pacific Coast Guard Forum is an excellent example of how otherwise militarily mistrustful countries can develop confidence-building measures through paramilitary agencies. As such, it does indeed, as you suggest, pose a potential template for the South China Sea.

There are, though, various barriers to the creation of a South China Sea Coast Guard Forum, primarily owing to the actors involved: China perceives a much greater benefit to be gained through coordination with the advanced and substantial coast guards of the North Pacific. By contrast, there are relatively few practical gains to be had from China engaging with the coast guards of most South-east Asian countries.

Nonetheless, as a confidence building measures (CBM), and one that could be driven by non-disputants such as Singapore, it is certainly a worthwhile suggestion and idea to pursue.