For an example of the external editor, refer to a program like mutt, a console email program that you’d find on just about any linux box. When you go to type an email, it launches whatever editor is listed in the EDITOR environmental variable. I don’t believe it ever stores a file - instead, it stores the text in a buffer and returns it to mutt when it’s done running.
I’m not sure how the buffer is passed… probably through a pipe, but that wouldn’t work on Windows. Some popular editors have a client/server mode or ftp mode - perhaps that could be used? I believe vim, emacs, and notepad++ all have this functionality.
It’s not really a feature I’d expect to ever get implemented, but as you probably know, most programmers love their editor more than their family, so it’d be an awesome present nonetheless.