I just had another idea. I really want registered post to be an option for customers (as many orders are only worth a few dollars anyway).
So this is my idea:
Duplicate the auspost php files and call it auspostregistered. Change all instances of auspost, to auspostregistered. There are 2 of these files:
/cart/includes/languages/english/modules/shipping/
/cart/includes/modules/shipping/
Then you could create a new gif file with the registered post logo on it. Located here:
/cart/includes/templates/template_default/icons/
Then basically, you install the new module within the admin panel, and manually add a handling fee of $2.50 (the registered post charge) and set 'handling fee' to hide.
So in effect, this new module simply uses the regular post DRC thing to check the normal postage price, and then adds in the registered post charge of $2.50.
So if this were to all work, your customers are given the chance to select either regular post, or registered post. Ive tested this through the checkout process and it seems to work perfectly fine - but I could be wrong.