Applying advance payment to Purch. Invoice service tax

Dear Experts,

Please suggest how to settle an invoice which has service tax(GTA) on it with an advance payment made. I mean that if I apply the advance payment to purchase invoice with service tax before posting then the service tax payable should directly go to "service tax payable" rather than going to "service tax payable(interim)".

Please suggest. Excuse me for insisting, but its really urgent. [-o<