For anyone else who has been looking for this function, it’s been added in UE 4.3. Here’s how to use it:
Add Reroute Node… now shows up in the context menu when you click-drag off of a pin; you
can make connections to a reroute pin like normal, move it around (by dragging near it or ctrl +
dragging on it), and remove it by Alt + Clicking.
You can also put comments on a reroute node by double-clicking on the draggable area below,
or hitting F2.