Extreme cellists hit the roof

I've had my attention drawn to the Extreme Cellists. They are a group of cellists who specialise in playing in awkward and remote places. They are doing a tour to raise money for charity playing on the roofs of 42 different Cathedrals (!!!!). The details of the tour are here. If humanly possible I want to be at St. Paul's or Southwark, if only for the curiosity of it.