Probably through Harvard's 2+2 program, which accepted its first class in 2009. The 2+2 program permits undergrads to apply to HBS. If accepted, you agree to work 2 years then go to HBS for 2 years.

I've had a couple of friends that were accepted in 2009, and they speculated the 2+2 program had as high as a 30% acceptance rate in its inaugural year since it wasn't well publicized.

That's my guess.