Over Delivery Tolerance on Classic PO confirmations w/o Materials

Dear Gurus

We are running SRM7.01 with Classic scenario deployment. We do not use productIDs/Material Master in SRM: Only adhoc or catalog items.

We have a need to introduce over-delivery tolerance for our confirmations in ECC.

Could you please advise how this can be done for classic if no material masters are used when the PO gets created in ECC?

Thanks

Ian