You could just change the rim to a GT-Spec or Prova D-shaped rim. That's what I did. Quick and easy to do. You would have to carefully disconnect the airbag cables with a dental pick or tiny screw driver.
From what i;ve understood the 15+ steering wheel should work just fine on the 08-14s. The airbag though would not transfer from a 2011 to the new steering wheel. At least that's what the dealership says. I'm in the same boat as you. I've got a 2011 sti and i really like the look of the 15+ d-shaped wheel. I'd rather have it than the prova or dam-d. The problem is that you can find the rim and controls for the 15+ wheel on ebay for like $200-300 but the center piece which includes the air bag is like 500-700 depending on where you go. All the answers I've gotten back it looks like you'll be in to it $800-1000 depending on what deals you can get. Unless you can find someone selling the entire set up you'll have to buy the two pieces. Let me know if you end up doing it. I've put that towards the end of my build list at this point.
So after trying every possible way we could think of the answer is technically no. It doesn't fit. Not unless you want to pull and swap your entire steering column. Which isn't a direct fit and will require custom fab to make work.