In the event that the Attorney General has refused to certify scope of office or employment under this section, the employee may at any time before trial petition the court to find and certify that the employee was acting within the scope of his office or employment. Upon such certification by the court, such action or proceeding shall be deemed to be an action or proceeding brought against the United States under the provisions of this title and all references thereto, and the United States shall be substituted as the party defendant. A copy of the petition shall be served upon the United States in accordance with the provisions of Rule 4(d)(4)