According to Wikipedia the M roadster has the engine imported from Germany but the car is still manufactured at Spartanburg. (Wikipedia isn't always correct though)
http://en.wikipedia.org/wiki/Bmw_m_roadster
I also spoke to Canadian Customs and paying the duty doesn't depend on the VIN, but rather the country of origin. They told me if there is a faceplate that says "Made in USA" then I don't need to do the paperwork of form B232 which needs to be completed by BMW to state that the car was manufactured in the States.
Roland