Dante is the creator of the DC training method, cycles for pennies, blasting and cruising, etc.
'extreme stretches' are a part of his DC training method. they work quite well in my experience.
however, they are designed to stretch the fascia surrounding muscle tissue to promote growth and recovery.
they are not designed to widen your clavicles.. as that would be impossible, save for some bizarre surgical procedure..
I see lots of rear delt work, lateral delt work, and incline barbell bench press in your future.
also, avoid training your obliques, as they give the waist area a 'broadened' appearance.
I stopped squatting with a bar a short while ago, and I can already see a difference in the size of my obliques.