I had a horrible GPA but I didn't bother with classes either, just focused on the GMAT. I didn't do quite as well as Dukes w/ respect to the places I was admitted or dinged, but I really never felt that my GPA was that big of a deal because I've been out of school for so long.
The thing is, I think that for the schools that would really care about a low GPA (mostly ultra-elites), they're worried about low GPA's because that says to them, "This person hasn't always been a superstar." Doing supplemental classes won't change the fact that you weren't a superstar as an undergrad. Supplemental classes might take care of any doubts they have as to your academic potential, but a good GMAT score will do the same thing.
Obviously I'm not an admissions officer and I don't know how they all operate, but I really don't like the idea of alternative transcripts because I think it's crazy to jump through hoops like that, almost the same as joining a volunteer organization just for the sake of putting it on school applications. They're both really the same, they're easy things that anyone can do (and yes I believe anyone can take classes and get A's).
I'm sure many people would disagree with me on this.