Talk to the chemistry department at the school you are interested in getting into - in many cases, all you will really need to do is take some chemistry background courses. Depending on how much chemistry you've already had, you might be able to get into a program by taking 2 or 3 semesters of extra undergraduate work. If they will transfer all of your other credits, that might even add up to a second BS.
If you combine this with some undergraduate research, that will give you a step up trying to get a PhD advisor - at the very least you'll get to meet (or at least learn about) all of the faculty and how they treat their grad students. If everything works out, you'll step straight into your undergraduate research advisor's graduate lab with part of your work already under your belt.
It does add an extra year or two to your graduate program, but if you really want to go into chemistry and don't need to go straight to grad school from undergrad to keep your student loans going, it might be worth it.