How is the first animation in this thread accomplished? I can get the IK constraint to move a path like Stretchyman, but can't seem to figure out how to scale the IK bones up when the IK constraint is moved (ie stretch the path)

It's a bunch of bones constrained by a path, constrained by an IK. To make the IK stretchy it's in turn also constrained by the path

Can somebody elaborate a little more on this? I've got a path and IK constraint setup just like the stretchyman project, and it works as expected, but when I translate the IK constraint past the maximum length of the IK bones, the path does not stretch to where I've dragged the IK. I'm not sure exactly how to "constrain the the ik to the path" to make it stretch.