There's only one plugin that people actually use, Flash, and that runs in a NaCl sandbox anyway. So there is no need for any hacks to get this to work.
Flash runs in the Pepper/PPAPI sandbox, not NaCl. Your confusion is understandable, however, since the first version of Pepper was the browser API layer for NaCl. The difference is that NaCl applies an inner sandbox layer that's much stricter than the sandbox used for Pepper Flash (or normal Chrome web content for that matter).
Ah, interesting. At least reading the public Pepper docs, it seems like there is a hook where the browser requests audio from the plugin/NaCl app/whatever. Is that how Flash gets its audio data into the host's audio subsystem?
