Actually Wilson, each school requires you to advise them whether or not you would be willing to consider BMP, CSP and/or MRBS (though for MRBS it's really an application). This isn't just at UNSW but at all schools.
Thus, if you don't want a BMP then you just say you would not consider it. When the school comes to offer BMPs they look at the list and see who is eligible that said they would consider it, if you're there they offer it to you. If you're eligible but said you wouldn't consider it, then you just don't get an offer.
As for the quality of candidature, nobody has ever tried to use my bonded place against me. But that's because they think I know everything.
See what a year of uni does? It makes you a god of wisdom in the eyes of mere school leavers, even those elite 99.95 med students.