I think this is a great idea and I have worked with dual enrollment (high school and college credit) courses in the past. You could mention that college is quite expensive and having more credits when you enter a four-year university would make life easier for you (and your parents, I'm assuming) financially. Furthermore, the more credits you have as an incoming freshman, the less likely you are to drop out. Being in a familiar environment while you transition your way into rigorous college work would make the transition less stressful when you get to the four-year school. Also, it seems to me as though you need to be challenged. All too often senior year of high school is spent not taking rigorous classes. You need hard classes now more than ever because it is easier to keep the brain stimulated than to try to stimulate a resting brain.
Hope that helps and best of luck to you! This sounds like a great idea.