If you can bring me a single drop of his blood I can build some crystals, like the ones I use to pretty much prevent my magic from doing the same thing, special for him to do the same thing for him. It'll help keep people from getting hurt, until he learns control.
I'll also see if Henry can read up on his father's notes and see if there's any runes or written spells that might help too, because so far runes and stuff aren't backfiring.