Australia Post Api Using Contract Rates

It seems that the shipping method for the Live Australia Post uses an API for use by non-contract merchants only. It doesn't estimate shipment prices for contract merchants. There can be substantial pricing differences between one's own contract rates and non-contract merchants which I understand is what the CS-Cart/Australia Post API does. I checked the rates on Australia Post's shipping calculator and it is indeed the non-contract rates. The problem is that the higher non-contract shipping price is enough to scare away customers.

This is what I received from Australia Post themselves:

Our Enterprise offers two APIs in this space;

1. Estimate Shipment Prices – For contract merchants only. Part of the suite my team support.
2. Postage Assessment Calculator API – For use by non-contract merchants only.

I have been asked by a number of vendors wanting to use their own Australia Post rates as they are far more competitive.

Is there a way to use one's own contract rates using the CS-cart Live Australia Post API?