Genrating pegging for GATP - Sales orders to reciept elements

Hi, We have a requirement to get the sales order number in the planned orders which were used to confirmed the sale order,after the GATP check,this can only come through pegging relationship, but in the current design this information is not coming in the planned orders.

We are using planning strategy 40 in ECC and we can not use fixed pegging in our ATP check.

Please suggest any work around to get the this information in the receipt elements.

Thanks,

Vinay