This is going to sound harsher than I mean it to be, but can't he just earn gold the hard way like all of us did at some point?

That being said, it would probably be better for him to call or write MR than for you to do it as his son. Secondhand requests are always easier to deny. Tell him to think again about the Visa, as I don't think you need pristine credit to qualify for one of those. And if you really want to help him out then pay for some weekend/leisure stays for him that he can credit to his own account!