I do believe modern Commodore's have anchor points behind all rear seats (any mechanic will be able to check for you), but you cannot use the anchor point from the centre if you wanted to put the seat on either side - you must use the one directly in line with where you wish to put the seat IFYWIM? Older models may well be different - tho depending on the car, extra anchor points can be fitted.

We've got our seat behind the passenger seat as well.... so much easier on my back and whilst I am not planning on any sort of accident, I do have faith in the side impact bars in my car.