He can use Menoxydine to prevent further hair loss for the front AND back of his head. But if he's experiencing loss of hair in the back ONLY he can use Propesha (sp?) / Rogaine. The increase in body hair on the back could be associated with higher levels of testosterone in his system, which is hormonal.

Does his hair loss and hair growth bother you?

I can help you to ease your problem. I will recommend you Aloe vera neem shampoo. Aloe Vera is recommended as a hair tonic to promote abundant and luxurious hair, Neem is used to soothe skin and scalp conditions, and Hibiscus nourishes hair at the roots, supporting maximum growth. Especially recommended for dry, thinning or perm-damaged hair.

A man with back hair growth and scalp hair loss is common in diabetic men and/or men whose mothers had PCOS. It can also be completely genetic. A physical and testing for insulin resistance would be the place to start.