I'm not suggesting that this would work for subverting an agreement as it pertains to work done while an employee. The grandparent specifically referred to an employer demanding past work, presumably predating any business relationship.
Your approach might be enough to win a lawsuit. But he probably can't afford to fight a lawsuit, so whether or not he'd eventually win doesn't matter. Even if he could, it would be a hollow victory. He'd get to keep his modestly successful iPhone game, but it would cost him his job and maybe a year's salary on lawyers, plus 2-3 years of aggravation.
