I think liuetenant was confused when the OP wrote, "commerce/science" but that notation is generally used for double degrees. I have already PM'ed Christiano about this, but as a general information, there are two way of approaching this:
1. If you do want to go to UoM regardless: Do either Arts or Environments where Methods isn't a pre-requisite. Do a subject called
MAST10012 Introduction to Mathematics which acts as a pre-requisite for Methods. And if you have achieved over the Clearly-In for either Science or Commerce, do a mid year transfer into either one and you will most likely be successful.
2. Go to another uni doing a course which doesn't have Methods as a pre-requisite. Preferably choose a course and a uni which allows you to complete a subject equivalent to Methods. Then do a mid-year or end of year transfer into a course of your choice at UoM.