Regarding Delivery date

Hello Gurus

I have a requriement that for a sales order quantity (MTO) say qty is 10 then the delivery date is confirmed as 26.11.2008 based on in house production days in Material Master now if i increase the quantity to say in another sales order or same sales order for qty 600 the delivery is poposed same as 26.11.2008 but i want that to change based on qty say like instead of 26.11.2008 atleast it should say 02.12.2008 or above or some date difference how it is possible

Thanks in advance