Caching content from other handlers



I am developing a module which includes a handler that I would like to
be able to cache the content of.

AFAIK you can only cache content passed to an upstream (using
proxy_cache directives) or fastcgi (using fastcgi_cache directives).

Is it possible, though, to cache content from a handler (installed by
another module), without proxying internally (i.e. without creating two
servers in the configuration file, with one passing to the other) yet.
If yes, what’s the API? If not, it this a planned feature?