I have to agree with Keygrip: Do the hour building when getting ready for the CPL.
Also, the JAA PPL will not even show on your CV when you apply to airlines because you will loose it upon gaining the CPL. The FAA PPL is yours to keep. - If you ever apply to an airline that flies beyond your little island, you will see that they do not object to international experience (some even require this). Some UK and European airlines even fly across the pond themselves
If you do decide on a more sensible route, you will do an FAA PPL, then a few hours over there to get the required Xcountries and night flights, etc out of your way that are needed for the JAA CPL. Remember that you do not need a night qualification with this route and make sure you get the FAA RT licence (no test, only a fee. All info on here).
Don't listen to those selling you services, but to those who have done this. And of course you do not need to be signed off for any flight you are licencensed to do.
cheers IP