A breadth track won't give you a qualification, but the subjects will be recorded on your academic transcript for any potential employer to see. As far as I know you can't minor in your breadth, because it's not part of your degree.
You can minor in your breadth.
I've got a Minor in Chemical Systems within my B.Comm.
At UoM? How do you do that? 
David Shallcross, the head of the Chem Eng department wrote a paper on the implementation of the Melbourne Model, and the implications it has/would have on the Chemical Eng department.
Here's a link to the paper-
http://search.informit.com.au/documentSummary;dn=591888686011012;res=IELENGIn the abstract, it lists the different pathways that you can go through to be admitted into the Masters program. He writes 'Students will be able to study towards a professional chemical engineering qualification by following several pathways including...a Bachelor of Commerce with a minor in Chemical Systems followed by a Masters of Engineering (Chemical).'
You can get a Minor in Chemical Systems whilst doing a B.Comm by doing -
Calculus 2
Linear Algebra
Chemistry 1+2
Engineering Mathematics
Transport Processes
Fluid Mechanics
Chemical Process Analysis 1+2
Engineering Systems Design 1