If the parties are unable to indicate from the outset the persons to be heard, the judge may nevertheless authorise them either to attend the enquiry without further formality with the witnesses they wish to have heard, or to inform the court registry, within a time limit set by the judge, of the surnames, first names and addresses of the persons they wish to be heard. When the enquiry is ordered ex officio, the judge, if he cannot indicate in his decision the names of the witnesses to be heard, shall enjoin the parties to proceed as provided in the preceding paragraph.