Change all prices in zone shipping module easily?

I have a situation where the cart I'm setting up will be in a different currency (USD) to my local currency (AUD). This means that i will be paying the shipping costs at my local post office in my local currency (AUD), but customers will be paying the postage as determined by zen-cart in USD. Sounds simple enough but the problem is when exchange rates change, I need to then change all the shipping prices in the zone shipping modules (there will be quite a few modules due to quite a few different shipping methods, about 200 different values in total). If there was a way of changing all the shipping prices by just changing a conversion rate somewhere it would be easy but I dont think there is an add on to achieve this?
I realise i could set all prices in AUD and use the currency factor but the reason I dont want to do that is the products will be purchased from the USA so if they are priced is USD then they will never change. If priced in AUD then they will need to be changed everytime a new shipment arrives according to the exchange rate.
The idea is to buy products in USD, sell the products in USD, recieve the funds in USD and be able to pay the suppliers in USD never having deal with exchange rates, only hassle is the postage as I cant pay for that in USD.

After sleeping on it I realised all thats needed is for the postage price to be multiplyed by a conversion factor. This figure will be what i can change to alter the shipping price of all zones and weights easily. I dont know anything about programming tho to be able to add to the zone shipping module the neccessary code to make it multiply the postage price by a number.

Can anyone help me out with this?

You would need to customize the Zone Rate zones shipping module to calculate in the amount you want to change the cost by so that you do not have to manually change each price ...

You might post in the Commercial Help Wanted if this is not something that you are familiar with doing ...