I think it's impossible to get there without natural talent. To me, the 10,000 hours of practice theory just doesn't work. Golf is a complete game, that has very strict and cruel facets. You must be average off the tee. You must be average in GIR. You must be way above average in up and downs, sand saves, and putts.
I liken it to Shaq when he played for the Heat, Lakers, Celtics, Magic...he was an awful free throw shooter and had zero range. He was able to flourish, win world titles, make millions of dollars, was an All-Star a hundred times over because of his tremendous size, length and athleticism. What he lacked was the hand/eye cooordination to be a good free throw shooter. Thankfully, he did enough things well that his poor foul shooting didn't hurt his team or career too much. If basketball was more like golf, Shaq would have never played. You can't have a single, glaring weakness in golf.
Liken the above example to the Dan Plan. If he puts in the time, practices, practices, practices (like he is) but is devoid of the natural talent needed to shoot low scores (hand/eye coordination) - then he will fail. He could probably get to a low single digit or maybe even a plus handicap on work ethic and repitition alone. However, does he possess the natural talent to play on tour. Probably not.