Adding a hood to my Nano puff Jacket?

There are local shops you can find that will do modifications to gear. They’d need to look at your specific hood. There is a local shop here in Seattle that will take mail in order repairs: http://rainypass.com/modifications/

Although the reason most folks will just buy a new one, is that the cost of that alternation will likely be more than buying a new jacket. That is unfortunately the nature of a mass production society. But I agree with your sentiment about not wanting to get rid of something that works fine. Though you likely could find a new owner for it.