Yes it is possible.
The above members who have said no it isn't possible and it's moronic etc are incorrect.
You need to talk to your school subject co-ordinator about this. Not all schools will allow you to pick up a subject halfway through prelim/at the start of year 12. It will depend on your school's willingness to assist you in doing this, their opinions on your ability etc. To complete a HSC course you need to have 'satisfactorily completed the prelim component' - to overcome this most schools that allow you to pick up a subject in year 12 will ask you to complete prelim assessments, or other requirements to meet this...You need to be willing to work hard to pick up a subject in year 12.
I recommend you talking to your subject co-ordinator straight away to find out whether your school would support you in this, and what sort of requirements you would have to meet etc. This is for 2 reasons:
1. There's no point worrying about/planning it if your school won't allow it
2. The sooner you decide and talk to your school the sooner you can get started on catching up