Hi Uday,
do you create the additional sales order quantity directly in ECC as a seperate line item or even a seperate sales order or do you create them in APO only?
In case of doing so in an ECC system, you can simply differentiate the requirement category (req. class) via customizing. Simply choose one req. category which is not consumption relevant.
In case you don't differentiate on ECC side or you simply create it in APO itself, I would suggest to manipulate the ATP checkmode during integration which will lead to the same result.
regards Peter