I've always wondered, do graduate schools really admit students from other disciplines by having them take defiency courses? or do they just say that as a "formality"?
In my experience, I've seen it happen where a student with a physics undergraduate degree, but no formal courses is plasma physics was admitted to the graduate program and allowed to take a senior undergraduate couse in plasma physics before continuing into the graduate class. So yes, it happens.
Our university had someone come in from engineering to be a physics MS student and I believe he was "strongly suggested" to take some of our undergrad courses. He left the department half way through that semester though so maybe there's a reason why people require them.
At my department people have been accepted without an undergraduate degree in math. They have often failed our placement exams and been told to take one or two undergraduate classes instead. However, they are still required to pass orals by the end of their second year. It means that if they can't take the grad level courses right away, they are pretty much screwed or they really really need to work like crazy in order to pass the orals.
I'm at a school, studying computer science with a math undergraduate degree. I have a couple of formal courses required of me before full admissions, but yes I'm in.
My school is a little weaker in terms of reputation though. It's likely you'll make it in anywhere as long as you're not applying to the highly competitive schools and your grades are decent.