I could be wrong but my understanding of FAR61.3 e, states that to fly IFR the pilot must have a valid instrument rating so a JAA / CAA IR would be necessary.
I have discussed this in the past with the FAA and that would appear to be their position.
I do take the point that an IMC rating is a national instrument rating and should not be underestimated as something "cheap" as would be the position of some on this forum.
It would suit me fine it I was wrong on this one.
Tony