Why would you even bother with this? You're getting way beyond my technical abilities, and because you are dealing with a com.au domain name, you are getting into very murky territory because AuDA is a rule unto itself ... from the little I know about this area (and in 8 years of web design/hosting/domain registrar I've never ever felt the need to do anything in this area), I think I can make the necessary changes for TLD domains (.com etc), but I've never seen anywhere near this technical access with the com.au names - I don't think they let us do it.
If I was you, I'd just forget about it, as probably 98% of web users still always type in the "www"