For a bit of research into lightning hitting people (not the best thing to search for) I remembered some of the Star Wars films and Mace Windu being electrocuted by the Emperor in Revenge of the Sith.
This video really helped me with my movements and how he has a couple of key poses and uses his shoulders to move alot. This means that the Guard must have some rotation in his body not merely shaking and the arms move up and down.
It did also show me that if the lightning is done effectively then his poses may not be seen too much, although from the side view I am doing they may be.
So he must shake, which I will try on twos, but move to two or three key positions whilst shaking throughout. As this is for an animated piece rather than film I will exaggerate the movements more than what Mace did so they look effective and also provide a stark contrast to the slow small movements of the Guard beforehand.