No. If you do 11 units, and bomb out completely in Business Studies, only 1 unit of Business Studies will be included, which is the equivalent of (internal assessment + external HSC) / 2 and then halved again.
So from what I know both HSC mark and internal are inseparable. For example, you can't just count your internal mark - or your HSC mark. Both have to be combined, averaged, and the halved again (if they are to include 1 unit of a normally 2 unit subject).