Personally, if I knew they were going to be in for that long I would have put the stop lines in when they were first erected. That said, how much life have they got left?
“(3) Where no stop line has been provided in conjunction with light signals or the stop line is not visible, references in relation to those signals to the “stop line” are:
(a) in a case where the sign shown in diagram 7011, 7011.1, 7011.2 or 7027 is placed in conjunction with the light signals, to be treated as references to that sign; and
(b) in any other case, to be treated as references to the post or other structure on which the primary signals are mounted.”
… so you’re covered with the signs.