To be honest, there are purely logistical reasons as to why there isn't a combined degree with courses run at the conservatorium- classes are held at the con and classes for science are on main campus. You would have to travel between campuses which would take up probably an hour timeslot- eg. you wouldn't be able to have a class at the con going from 9-10 and then be able to get to a course at main campus at 10. Science would be even more difficult to combine with then, say, an arts degree, because there are so much more hours- there are pracs etc.
I have a friend that did a music course at the con combined with law but because her classes were at the con she wasn't able to make enough law classes back at main campus. She was basically told just to defer the law subjects, and although she is still doing a 'combined law degree' she didn't do any law subjects in her undergrad and then just went into the grad Bachelor of law stream after she finished her first degree.
I don't see them introducing a set combined degree anytime soon- the logistics are difficult to overcome and in any case, there may always be clashes whether it is a set combined degree or not. Eg. I do arts/law but if I chose a particular arts subject that clashed a particular law subject, they wouldn't move things around, I would have to either choose to do both subjects and skip lectures, or drop/change the arts subject. This may even happen, for example, if you did BScience and BArts majoring in music. Just because you are doing this degree doesn't mean that science classes and music classes (that may be held at the con) won't clash...I have met people who haven't been able to do particular subjects due to clashes- generally there isn't much the uni will do to help- you just have the options given above (and it sucks, but that's life).
I guess you just have to figure out what you want to do- however it doesn't have to be set in stone. I have another friend that got into music performance at the con. She spent a year there then decided it wasn't for her and transferred to law at main campus (she's now a lawyer, but still plays for fun in orchestra's and stuff).