Yes you can. The FAA allow flight outside of the USA on a foreign licence with the full privileges of that licence. They now consider Europe to be one 'country' as far as licensing is concerned so will allow flight of an N Reg by a foreign licence holder around Europe. As part of a 'project' I have undertaken recently I have written to each of the JAA/EASA countries CAA's and asked for clarification on their policy. Every response has been that they are happy with it.
So the holder of a JAA licence may fly an N-reg outside of the USA on a JAA licence without the need for a piggy back licence. This includes flight under IFR in CAS if the JAA holder also has a JAA IR.