I also tried to get around prereqs in college (for EE rather than CS) and I was told by the professor that "It would not be good for the university." I believe my university had previously been in trouble with ABET, the accrediting organization, perhaps for the very issue of being too lenient with prerequisites. Apparently ABET wasn't invented to give people opportunities to learn, but to control who has those opportunities based on arbitrary criteria (like GPA).