Ya , as per my knowledge just using ECC its not possible to have functanility of make to stock with configurable material.
as i replied earlier , in the customizing transaction OPPS you can get requirement class for this group. In the transaction OVZG you can check in the field "Cnfg." if for this requirement class a configuration is mandatory 
or a configuration is allowed (*).
Its as good as having custome rindependent functionality for PIR , not sure how it works and behave, as never did it myself.
Thanks
Ritesh