I strongly recommend Dr. Leon Root's book Oh my aching back. I used it to understand the anatomy and kinesiology of my back. Once you know how it is designed and works you can begin doing the things that will stabilize it and give it a chance to heal. The book Posture Alignment by D'Arezzo should also be studied.
I haven't though about my 'bad back' for years. But know this, when I was going through the pain and inability to stand up straight I never imagined I would be care free again in my life time. It took a couple of year before I wasn't thinking about or worrying about by back. The last 10 years it doesn't even cross my mind, true peace :)
There are links to the books by Dr. Root on my site, www.DanzanRyu.com/books.html#restoration. The book I used is out of print, I imagine the new book is improved.
Bottom line: educate yourself then take action. You have to develop strength and flexibility in addition to removing/minimizing the things that resulted in a broken back.
With the education you can structure a yoga program that will be beneficial. Many of the therapy exercises are also yoga exercises. But yoga is so much more than the physical, it is like Qigong, put your mind and intention into the body and breath. Simply going to a class that is labeled yoga will not do it, you have to have the mental intention a yogic approach to whatever you do.
Restoration Therapy is also very helpful if the person is in a serious program to change their body.
Make sure he knows that difference between pain and injury. My hip surgeon told me that the body will not allow you to do things that will injure the body, you can ignore the pain.