They ALL do.
There's no such thing, in reality, it's just a case of doing your flying training with them - to include all aspects of both the FAA and the JAA requirements - with two sets of written examinations and two sets of flight tests with two examiners.
There are no dual rated examiners yet - so you need to fly with both. I've heard it said that some FAA guys will sit in the back on your JAA test and examine you from the back seat at the same time. Not very professional - and I wonder what would happen if one guy said you passed, but the other said you didn't.