What I have done when I was faced with this situation was to just click on 6 and then create a new node. Pick that up and lay it right on top of 3. I do not know of a way to create a branch like what you are looking for but if you plan to stroke the path it should look fine doing what I said. Furthermore, if RobA doesn't know how to do it, then it probably isn't there. He's sort of the Gimp expert.

I am usually just happy when my paths work at all.