Mr Fixer
Im not so sure you cant use narrow bodys for this type of service. Both Airbus and Boeing, with their BBJ, have smaller narrow body aircraft, in a buisinesst class fit, with the ability to do UK to JFK. I believe Mr Branson is looking into this area. I also believe Monarch and A2000 have vastly reduced seat numbers in some of their 757's operating for the upper end of the market.
It's not the width of the aircraft that counts its the amount of personal space you have inside.