Personally, I think you're far too concerned about a matter that is of relatively trivial concern. for the purposes of MBA admissions, what is far more important than what specific courses you took in college is what your work experience is. Hence, I would be doing whatever it takes to get that work experience. For example, that could mean doing part-time internships or co-ops.
The truth is, you don't really need to know that much math to complete most MBA courses. Would math be useful, and probably get you better grades? Sure. But it doesn't really matter that much anyway, because the truth is, most MBA employers don't care very much about your grades anyway, and will hire you (or not) based on far more arbitrary criteria. Furthermore, a number of top MBA programs such as Stanford still practice grade nondisclosure, which means that prospective employers don't get to see your grades anyway. Now, it is true that law school employers do care about grades intently, but it seems to me that you would not have to present your MBA grades to them (just your law school grades).