Hello Tamil,
i am not sure, but i think your requirement is not SRM standard.
Invoice (without accounting document) is created by supplier itself in his "own portal" (equivalent to the sell-side in Supplier Life-Cycle management). Then, this invoice is sent to SRM for replication into ECC.
So, from this point of view, there is no business reason to allow customer (from supplier point of view) to create sale document (from supplier point of view) in supplier "portal".
Regards.
Laurent.