The best thing you can do....the day you find out what classes you will be taking, e-mail your professors and tell them your situation. Many of them will be gracious enough to let you take your finals early. It might also be wise to schedule your last quarter with some easy classes, or with classes you know do not have finals exams. You could even e-mail professors ahead of time before you enroll in classes.
You can definitely not get away with waiting till the last month of school and then spring it on your professor. I guarantee they will not be okay with this. You have to communicate as soon as possible. You might see if your corps director would be willing to write a letter to your professors as well explaining why you need to be there early, if they are unsupportive.
Also if you can afford it, you can always fly up on weekends between classes