I guess that the only way that a school could prevent you from working is to not offer you any work-study aid. I've known several people who were able to hold down a job in med school, but of course their hours dwindled as the semester went on. Also, why not teach on a flexible schedule for Kaplan, TPR, etc.
And although the book is a bit dated, I found it interesting how a classmate of Robert Marion's (in "Learning to Play God") held down a full time job in Connecticut and was able to return to Bronx, NY the night before a test, only attending exams and studying on his own.