Assuming you have SketchyPhysics 3 experimental (SP3 X), you can use onTouch to help with this. First, instead of a spring, use a slider, set a fixed value (0) as the controller, and play with the accel and damp until you get it satisfyingly springy. You can then replace the controller with a variable, e.g. getVar("spring",0)
Then, in onTouch of the same object, use setVar("spring",1)
This means that when the object is touched, the 'default' position of the springy slider will move from the 0 position to the 1 position.