As a serving ATCO I am in no doubt re the rules concerning 'vectors below the RVC' you cannot give them. Even a suggested heading is taboo. Ask the pilot to report a level passing the base of the RVC, identify him then vector him. If he wants to know where he is try to give him a position to a location and then say 'own navigation report' ' then ask for a position within cover. I believe that it is an automatic ticket pull by the ATCEB if you give vectors below the RVC.