Gayle, It sounds like you are already giving the obvious additions to his diet (avocado and coconut). I just wanted to add that in researching hair loss in people, an insufficient amount of protein causes the hair follicles to shed an over abundance of hair which can make hair thin or break off. I KNOW these guys don't typically eat protein, but have been known to ransack a bird nest and consume the eggs, if given the opportunity. My dwarf, Joey lost almost all the hair on his stomach. About 6 months ago I started adding chicken or turkey babyfood to his vegetable babyfood. He now has hair that has grown in on his chest and on his lower belly. I don't know if there is a correlation or not, but Dr. E told me to offer him chicken about a year ago, so I did. The addition of the meat babyfood was just in the last 6 months. He's still super picky but he eats little pieces of chicken and sugar snap peas on his own. I just wanted to share what I've observed in my situation.
I also do believe stress factors in to hair loss, much the same way cats and dogs shed a ton of hair when you take them to the vet.