SRM 7.0 - Limit what purchase order a Buyer can see in the POWL list...

We are upgrading to SRM 7.0 extended classic from SRM 4.0 classic.

Is there a BADI or enhancment I can make to limit what purchase orders the buyer can see and ultimately change in the POWL purchase order list?

Our buyers are limited on what purchase orders they can process beased on data in a custom field..

Thanks,

-Paul