Depends how much of a detour you want, but you could head up the A2 to come off at Bluewater, quick blast around there down into Darenth, then through Sutton at Hone to Farningham then Eynesford. The Eynesford to Otford road is lovely. Then a quick jaunt round the back of Sevenoaks to Tunbridge Wells.
Sorry to piggyback off this... I'm taking the girlfriend to Tonbridge for the weekend (hence I'm still a maybe for PoL, depends how she feels on the day really!), Have any of you guys recommendations around the Tunbridge Wells/Tonbridge area to visit?