The battle for a six pack is more won in the kitchen than in the gym to be honest. In order to have a decent six pack you'll need to be at 10% bodyfat or less. Find somehwere online where you can work out what his maintenence calories per day are for him and then make up a diet that is approx 500 calories short of the maintenece level. Follow that up with at least 3 sessions of 30 minutes cardiovascular training and some stomach/oblique crunches and you'll be rocking and rolling all the way to the laundrette.