Ok, then I understand your reply.
My point is that there is nothing in the JAR regulation that states you cannot log flying time in an N-reg plane.
There is a problem flying as PIC in USA without an FAA license, but that's actually a USA problem and not an N-reg problem.
I know many people who flies N-reg planes in Europe on a solely a JAR license.
Under FAA rules you can log "safety pilot" hours. Under JAA rules the plane must be 2-pilot approved to log co-pilot hours.
It is not true that small planes cannot be 2-pilot approved. I know of a P68-Partenavia and a C421-Golden Eagle that's 2-pilot approved. It has nothing to do with weight. You can get a C172 2-pilot OPS approved if you want to.
The interesting question though is if you can log Co-pilot time on an N-reg, in USA, without an FAA license. Since you are not PIC FAA should be happy, but I'm not certain about this.