Firsr save the script in script folder of your project then

- AUTO STRETCHY IK CHAIN -
This script will automate the task of making a joint chain stretchy. 

The joint chain will stretch when the ik handle is pulled beyond its maximum length.

Directions: Select an ik handle. Click 'Make Stretchy'.

Basic Procedure: First the script will find the joints being controlled by// the ik handle that was selected.
The script will calulate the length of the chain. 
Two group nodes are point constrained to the base joint and the ik handle.
The distance between these two groups is calculated in a distanceBetween render node.
The chain length is fed into a condition and multi/div render node where it is divided by the distance.
The result of the division is plugged into the scaleX of each joint in the chain. This causes the joints to stretch.