Actually we don't have to hand-wave anything on perform -- I forgot about the existence of Versatile (OA) and Apprentice (DMGII) feats; Apprentice (Entertainer Barkeep, not that far off) would give him Diplomacy/Perform. It fits with his recent history working for his uncle and certainly makes more sense than him taking Martial Study/White Raven. (He may still take Martial Study at some point, if he's got room, but it'd come later.)

I've updated his sheet with the single-class focus.