TheRealStig:
Unfortunately, taking HBX courses is not going to change your GPA. It's a minor nice-to-have on an application, but will not be viewed anywhere on the same level as your undergraduate studies. The GMAT and any other ways you can demonstrate technical aptitude are the only bona fide ways to mitigate a lower GPA. You should also try your best to come up with a valid reason in your optional essay as to why your GPA is lower than average if you want to stand a chance at these top programs.
BoundMan:
Yes, they do. The admissions committees are all of these schools have their own processes for comparing GPAs from non-US schools. In fact, the same issue presents itself even within the U.S. Not every university, school within a university, major, coursework within a major, and so on is the same. These admissions offices are very meticulous in building an evaluation method for understanding your academic performance on an absolute and relative basis. If you are applying from an international school or there is something unusual about your GPA, you should can contact the admissions office directly with any inquiries about how it should be handled in your application and/or note that peculiarity that in the optional essay for each school.