Why can't you just take math and science courses at the same time? Everything is essentially a sequence course, and will thus take a year to complete. I know I wouldn't want to get stuck taking bio, chem, o chem, and physics all at the same time....I think my brain may have exploded. Plus, they are time consuming. I don't think you would have any time to do anything else because you would either be in class, in lab, studying or sleeping.
You can take bio and chem along with your math classes your first semester (this is what almost everyone I went to school with did). The don't require much math beyond basic algebra, and you should have had at least that in high school. Plus, it gives you a basic set up for future courses (first and second semester will be the same sequence courses, third and fourth semester will be similar but with more advanced classes). Don't forget about your electives too...but at least those classes can be put in anywhere. But don't forget about them and then have to cram them all into a semester.