Hi
If I were you, I would just do my hour building and then return to the Uk to complete your atp and cpl/multi ir. You can do your multi Ir over in the states but you will have to convert from an Icao or if you do the Jaa you will still have to do some training in the Uk as from what I have heard their procedures are slightly different. I will warn you that if you do the course in the states choose your school very carefully as there are a few JAA schools which are not really up to scratch according to uk companies. This is really based on rumours Ive heard so I would do some further reserch.
Ciao bl