Maybe use the Australia Post label option?     If you have an ebay satchel instead of a aust post satchel (not the prepaid ones) I am sure that Australia Post don't care.  

Then you can put it any address you like.

But you do run the risk of not being covered either by paypal or ebay.     

A more fiddly way is to talk to your buyer about refunding the money to them, so that they can send the money again with the correct address they want.     But some buyers resent this.