CS Cart Fractional orders

Hello There. I need a custom addon written for CS Cart. Ability for administrator to specify the possible fractional values of the quantity. In the admin back-end on product editing page administrator will be able to specify fractional Minimum order quantity (e.g. 0.1), Maximum order quantity, Quantity step and List quantity count. Ability for customers to choose the necessary fractional value from the drop-down list on product details page. See the screenshot below: It is preferred that this is hook based rather than core files modifications to make it upgrade proof in the future.