I feel for you! As a parent, I am very protective of my children...but as a child I was very "independent" (OK, I was an awkward little.....) and insisted that my diabetes was not going to make me "special" so did my own injections for the age of 6. The key thing was though, I wanted to,..if someone had forced me, there was no way I would have complied! The other thing to bear in mind, this was the 1980s, where you had the same dose everyday...so in that respect it was easier then.
Again,encourage gentley, at home, when he is the mood, but not push him into doing it. He is going to have to do it some day, but if you are happy to help, then it needent be today.