Fixed pegging in SAP ECC

hi,

Is there a way to fix the pegging relationship between a procurement element to it's demand. I know it is possible in APO , but is it possible in ECC.

We have a situation that one team creates a forecast well in advance and get their POs in time. We don't want any late changes to consume these POs and cause shortages for the demand. If the pegging is locked, system won't pegg a procurement element to another demand just becuase the date lies in front.

thanks

Rav