My initial brainstorm: A group pin would reside along-side the “normal” pins. The difference would be that the group pin would have a user changeable label that could represent a group of related PIN . Mousing-over a “group” PIN would drop-down a list of the PINs residing in the group. Dragging the mouse over a group member (pin) and releasing the button would activate the individual PIN.
Anyway, the drop-down feature would have to be implemented so that the member PINs continue to support drag-n-drop linking. Since a group pin button is only a labeled container for individual pins, the button itself would not support drag-n-drop linking. However the user would be able to drag-n-drop an existing pin onto the group button to add it to the group. The user should also be able to drag a member pin out of a group and drop it as a standalone, or drop it into a different group.
Maybe a PIN could reside in multiple groups?