Have your actor make his hair very unkempt and smoosh his face up against a piece of glass (a window does nicely). Take a close-up still of his distorted face (neck up, no clothes) from the other side. Print an 8x10 or so (lifesize) of the face and put it in a large jar so the paper follows the curve of the jar. Fill the jar with liquid and with the right light, distance, etc., it will look like a severed head in a jar. Stick the jar in a fish tank and it might work. No doubt some photoshopping will be required.
Good luck with your film.