You need a full or stand alone FAA PPL(H), with a based on license you're only allowed to fly the types that are on your JAA PPL(H), so useless.
To get a FAA PPL(H) you need to sit a written (computer) exam, and do at least three hours of training with a FAA CFI(H), then you 'might' (depends on your skill level, an instructor won't sign you off if it's marginal, because if you fail his pass-rate will be down, and can get the instructor in trouble) get an endorsment for the checkride, which you take with a DPE, after that you will have a temporary license issued on the spot. Furthermore you'll need TSA clearance which is not to hard to get, but takes a bit of time.
www.flightschoolcandidates.gov
As said before nobody will let you fly a twin-turbine or any turbine for that matter with low hours, so it makes absolutely no-sense