Doing upper division pre-requisites for a second master's degree - need advice
An anecdotal answer -

I am in an identical situation; I had done a bachelors in business admin and then an M.A. in economics.

My passion later turned out to be mathematics and I was unable to get admitted to an undergraduate program (or at least one where they would allow me to skip the electives).

What I did to overcome this was select some universities I wanted to attend and made appointments with the graduate program directors. I then went to see them in person and explained my situation and what I was hoping to accomplish. I then asked what options would be available to someone in my situation.

One of the graduate directors was very receptive to my case and admitted me into something called a "Qualifying year." I am technically a graduate student, but will be taking upper-level undergraduate courses for a year to get the background necessary for graduate level course-work. After this year, I have the option to apply to transfer into the full graduate program or apply to a different university.

A similar option may be available to you, though I imagine every university handles these things differently. Could be worth just going in and asking.