Alternatively, an FAA Class 1 may count as the initial Class 1, and then one can do a renewal in JAA land
Now that would be VERY interesting....seeing as the AME I go to in the UK is authorized to do FAA Class 1 exams, and JAA Class 1 renewals (as well as the JAA class 2s of course)
A friend of mine did the JAA Class 1 while holding an FAA ATP / Class 1 and I *believe* some of the tests were omitted, though he still did it at Gatwick.