Hmm, how about.... you all need to be part of a "militia" in order to own firearms. That way you have a purpose for their ownership, and you have some human contact to spot the crazy ones.
Then, in addition to being in part of a militia, we should make it be "well-
regulated", so we can slap some laws on that shit about what actually constitutes a militia - it can't just be one dude by his lonesome, and he has to do militia-things with his guns, he can't just stroke them in his basement until he's ready to die for some goofy reason in a movie theatre or a church or club.
Oh and hey - given that's already the requirement in the 2nd amendment - we don't have to change anything!
...Except, you know, the part about getting you guys to do what the constitution requires