Another option could be to open a UNIX socket in the privileged sudo process, spawn an unprivileged child process 'shim' that connects to that socket, and then the sudo process can pass the file descriptor over the socket. Since the child shim is 'clean', it should have nothing more than stdin/out/err open, plus now this passed FD. Then the shim can spawn the target program and allow it to inherit just the passed FD.

I think the larger issue is that I doubt many (if any?) editors allow opening a file via an inherited file descriptor! I guess some will read stdin (the shim could close stdin and then dup2() it into its place), but then there's no way to save the file back when finished.