I would do HES. I know several friends who have taken classes there to raise GPA for medical school and were successful in gaining admission after doing well at HES. Some of them were doing it full-time and some were doing it part-time. All of them were taking only science classes (biology, chemistry, physics) and did really well in them.
Obviously you will need to take only science classes and your grades will need to be as high as possible (I would say no lower than a 3.7) to be worth it.