According to the FAR's the ONLY validation that the FAA will ever give you is a PRIVATE.
You can have Private, Multi, Sea, Glider, Balloon or anything else BUT you ONLY have a PRIVATE.
You can do a short written to enable you to use your foreign Instrument rating as long as it stays valid in your home country.
So to sum up you cannot do instruction in an N registered airplane without a US CFI ticket.