it would be very helpful to simply implement cooperation with an external editor in a better way.
Have you clicked the "use external editor" button in preferences? It apparently causes the IDE to re-read the file(s) every time you do a "verify" or "upload" operation, and it prevents you from changing the code in the IDE window itself. I find that it works unexpectedly well for such a simple hack; you do have to remember to "save" your work from the other editor before clicking the upload/verify button, but ... no editor knowledge required on the arduino side, no arduino knowledge on the editor side. Brilliantly simple.