You are absolutely right. And this is going to be my main focus. However he wants to hear more than "stop drinking beer and soda and eating chips..." He knows he is sore because his belley is too big. So I have his mind on that. My initial thought is to work on bodyweight squats, plank holds on elbows, supermans, dead hangs, and some spine mobility (superjoint type) exercises along with a diet overhaul. It is a HUGE deal for him to ask for help.
Eventually I will introduce the idea of sandbags, rocks in backpacks, and other more involved things. I have to start with baby steps.