Magento Product List in Category pages Sorted by QTY (stock)

Hi, We are looking for a programmer to create a simple module that will (by default) order the products displayed in any category by QTY, greater to less, so that our products with stock appear at the top of the product collection. This does NOT require to appear as an additional sort field, as we do not wish for customer's to see it. It is only to do this behaviour by default but maintain the existing sorting systems within Magento. We are using Magento 1.6.2.0. We would prefer for the developer to provide the code which we will install and test. We are developers ourselves. Thanks