You could give the plunger a "Drag & Drop" behaviour, set to "vertical". Also, give it a instance variable, "initialY" for example.
When drag starts, set "initialY" to its current Y.
When the dragging ends, apply an impulse to the pinball with the force of the dragged distance to the pinball (distance(plunger.x,plunger.y,plunger.x,plunger.initialY)).
Under the same event, reset the plunger to its initialY and enable physics again.
Sorry if not everything is clear, I don't have C2 available atm, but if you want, I can create a .capx for you later.