I think it would be considered a sharking attempt if you believe it's a sharking attempt, however, I can't imagine it would make much difference regardless of who you might tell. If it were me I'd wait until it was his turn and then I'd hide that cue ball if it bothered me that much, if he asked me for it I might address it with him then and there, but that would be like loading his gun and helping him point it at your head. His argument, and it's a valid one, is that he is away from the playing table, out of eye shot and the other players on other tables, or beer drinkers, etc... don't seem to bother you. It would be polite if he were a little more invested in the match, but being rude is generally not a rule violation.
Someone mentioned HLT rules a few posts ago, I believe in the APA there is an HLT rule about practicing on the tournament tables while a session is in progress or during time that aren't designated practice times. Anytime something like this even had a hint of starting up at the HLT's I've been a part of the referee quickly put an end to it, but in weekly play, at a bar or pool hall it's just something you'll probably have to live with. If he knows it bothers you you can probably expect the behavior to continue and likely to increase.