Some thoughts from me ...
Does he do a desk job? We desk jockeys all do it, sit at a desk and hunch over the keyboard and that doesn't help! - I'm doing it now... but not now lol - Awareness of your posture if you are at a desk is important to help correct back rounding - so think sitting up straight shoudler high and back & shoulders not rounded - Sitting on swiss ball at your desk helps but personally I don't cos I'd look a total plonker! Though I have seen it done. I very occassionally sit on a swiss ball on the computer at home though.
Do the stretch where you kneel down , hands on floor in front of head then sort of move hips back and shoulders to the floor so your back arches back and so you stretch upper back - hands on the floorin front means your upper back gets stretched - sort of opposite to a cat stretch if you see what I mean. Can also do it standing with hands on wall above head and then leanining forward to arch/stretch your upper back.
Lying on a foam roller to stretch upper back works well - Obviously you have to place it mid/upper back - Can do active stretch with this by rolling back and forth - A towel under your back does teh same thing.
As you say, pec strectches - maybe very light flys but going for a very full stretch rather than using them to shift any weight.
How about overhead squats - that will force the shoulders to loosen - you never see an Oly lifter with a hunched back.
Upper back work as said above to correct muscle imbalance...
Go and see an Oesteopath
