Not GP, but using a similar setup (.org.gpg files for textual private data, on top of encrypted partitions as well), and Emacs comes with an EasyPG interface; doesn't need an intermediate temporary plaintext file. It can also handle an encrypted .authinfo, .authinfo.gpg, and encrypted bits of configuration (.el.gpg).

That's one of the nice things about common/basic/widespread standards and tools: good compatibility and support.

Handling non-GPG encryption in a similar way should be possible too, but won't work out of the box.

Emacs has lisp for that, it prompts for a password on open. On save it encrypts it if it was changed.