Post held Invoice automatically once GR is posted

hello Guys,

need some guidance from you people  on one of business scenario.

We have PO with  GR bsd INV.   Usually  we receive invoice in advance from vendors, so accounts team posts the invoice for the respective PO.

since we havent posted any GR yet in SAP  for PO, we get below standard message  & our invoices will be kept in HOLD.

At this point we send notification to Person responsible for GR  to Post  GRN.  We will use Header text field in GRN to mainatin  HELD invoice number,

Now our requirement  is   once  GRN is posted  we want to  automatically    process the INVOICE Kept on HOLD.

i mean ,,  complete the  missing data  in invoice and  post automatically in background.

So is there any BAPI which i can make use of it.  Any suggestions are welcome.