The PPL is not qualifiued to decide that and also they are not qualified to provide instruction to bring the pilot up to the required standard. Taking that into consideration, it is hard to see where such a check completed by a PPL would ever stand up in court..........hence one would have to say that unless one uses an instructor it is pointless having such a check.
Where does it say that a pilot without an instructors rating cannot give instruction that is not required for the grant or renewal of a licence or rating.
If it does there will be a few training captains and airlines in trouble!