Returning to School for a Better Degree?

HerbieTMac asks: "I graduated a few years ago (AB '00) from a decent school. Having worked my myself quite nearly to death, I am now the proud owner of two bachelor's degrees in Economics and Public Policy. I also have put in a couple of years working as a Computer Science TA for the masters program. Being older and arguably wiser, I find that I don't really like where I am going and instead want to pursue a PhD in physics. The problem is that most PhD programs require an undergraduate degree in physics first. Or at least a significant amount of classwork in the field. Most of my physics knowledge has come from self-study and bumming class notes from friends. I'd love to go back to school and do the work for the AB but most schools won't accept applications for a second (in my case third) bachelor's degree. Has anyone else decided that they really didn't want to work with the first degree? How did you go about convincing a school that you are a good bet? Or even to let you do some preparatory course work?"