Is using an external editor possible?

With the release of the new beta build (visual improvements are pretty cool btw) I decided to ask, is there a possibility to use an external text editing program with the installable Twine? I find myself working with several passages at once a lot, and that's not very convenient with the built-in editor, 'cause you're to close each passage and search the other one each time you want to copy\paste\add something. Any other editor with tabs would be much more effective. As for now I'm using sublime3 with syntax highlighting and copy\paste each time I think I'm done with the passage.

P.S. btw afaik these's no way to use git to collaborate with anyone, am I right? I wish my friend could check\edit my poor language while I'm coding new parts of the story.