Why even get involved? It's not your problem is it? So why be a grass? So what if he ends up with 2 extra hours a week? Not coming out your pocket is it? Unless you're bumming the boss, I wouldn't even get involved. If for some reason you feel you REALLY have to, then say something to the guy in question - don't be a pussy and go behind his back, say it to his face.

Imagine how fucked off you'd be if the shoe was on the other foot...