Often a useful short cut to spiccato is to play détaché while raising the elbow slightly to change the angle of the bow to the string. Then maintain the same stroke, but let it start to leave the string.
The détaché stroke in the middle of the bow uses a fluid forearm action. As you move the action to the lower half notice that although the upper arm and fingers are more involved, the movement is still predominately forearm.
Notice that Fintan's right elbow moves freely.
As outlined in the Introduction to Spiccato the forearm action is most easily learnt in the middle of the bow....