is it possible to attach it to the side of the frame, the large triangle? use velcrow straps or a bundgy cord. only other thing i can think of would to attach it to your back, but it will get bent.
talk to your professors. art classroom often have alot of unused storage, maybe you can keep it in there office and get it before class. just explain your situation and see if they can help. or make a freind in you class and keep it in there car, it will suck if they don't show up, but hey you gotta suffer for your art inorder to learn how to make better art.