Limit Distance between Object and instantiated Prefab?

I've been seaching for this on google etc. but couldn't quite get what I want. I have an Empty in the scene that is always on mouse position. When I drag with the mouse the empty stops and another empty is instantiated which is now dragged by the mouse (somehow like a slingshot). I calculate the distance with Vector3.Distance but now want to limit it. My first thought was the Spring Joint. I'm assigning the connected Rigidbody at runtime but I still can drag it infinitely.

Is there a good way to do that? I'm sure it's something simple..