You can't sell the reservation, it's not transferable except for extreme cases (possibly like the death of the original holder).
What you could do is have them give you the money for it, configure it how they want it, then you take delivery and immediately sell it to them. I don't what, if any EV incentives are available in Australia, but I imagine you would forego those as well.
Just make sure that when it comes to money, you get the check before you place the order and make sure you're not the bank (ie. the one receiving payments against their loan). Money and family usually don't mix very well. Put something in writing just to be safe.