"Say, do you by any chance know how one could make the spark discharge in a particular direction rather than omnidirectionally?"
You'd need something to attract the spark in that direction. Older TV tubes do just that. The beam generator at the back of the tube is attracted to the plate behind the viewing surface of the tube, with electromagnets around the neck of the tube to steer the beam back & forth & up and down.
Could you attract a spark in one direction and pulse the attractor off & on to let the spark(s) fly past? I don't know.