I'm too lazy to write a tutorial but that is basically how it should be done. See if you can figure out how I did it. There must always be a node that can rotate the whole figure without needing to use the actual figure rotation feature.
That technique you used there is very common.. I'm fairly certain most people know about it.
I don't see how you would be able to implement that feature, though. Do you mean maybe having three types of nodes? The center node, the regular node, and then this new "rotation" node?
You can always go into the figure properties and change the angle from there and that will rotate anything around the center node.
Most of this type of thing should be added while making the stk figure, though. That's part of the fun of making styks is making it movable in this way.
Don't forget you can set lines to static so they won't have nodes showing when you have the tool. It's pretty common practice to make all of the lines in a figure static except for one that extends from the drag node so tha you can drag one handle to rotate the whole figure.