As the dad of a 15 year old, I feel for ya and I know exactly where you are coming from. My son doesn't hunt much (although he is going with me tomorrow) so I don't have that problem there but in other areas such as sports or girls, well whatever I say, forget it.
If I knew the answer, I would be a Dr. Phil and you would have to buy a book in order to find out, but in all seriousness, maybe an uUcle or a close adult friend can try to encourage him to at least try some other areas.
I realize you said your older son has already tried this approach, but that may still be too close a relative (sibling competiveness) for him to listen. I know this works with my son. I tell him something, in one ear and out the other. A coach tells him the exact same thing and all of the sudden it is (should I dare say this word) gospel.
Beyond that, I would have to say let him find his own way even if it the long way. I am afraid if he is practically forced to sit one of your stands, it will tarnish the accomplishment, from his perspective, if he does in fact score. But hey, you know your son and his specific personality whereas I am just generalizing.
But I do feel for what you are going through in that we all want to see our children succeed and become better than what we are, in all facets of life.
Fortunately, for my son, the bar is not set too high in this regard.
