to be honest, JFK-LHR is a short flight and not always worth (in my opinion) the extra miles over Y.
As an EXP you could get dinner and/or drinks at the Flagship Lounge, and if in Row 21 or the first row of MCE, it's a relatively quick flight across the pond and save 30,000 miles.
Of course, if the non-stop opens you could always get the J seat to ZRH which would allow you to sleep another hour or two compared to LHR...