When I was a math grad student, I technically could have gone through the process to get 1 or 2 CS courses approved to give credit toward my degree, but I never actually cared about the "credit" part, anyway. So, I did my regular course in the math department, taught for the math department, then hung out half the day in the CS department. I ended up auditing, and thoroughly half-assing, Algorithms 1, 2, and 3, Programming Languages, and Automata Theory. Still learned a lot, in spite of the half-assery.