According to the AIM Section 6, 4-6-8, the language to use with ATC is simply, "Negative RVSM." You have to say it on the request for an RVSM flight level, flight level change, or climb/descent through RVSM airspace. You must also say "Negative RVSM" on check-in if currently at an RVSM flight level.
NBAA provides a guide for navigating the RVSM approval process. This guidance is fairly new, and indicates that approval through a prior operator of the airplane is acceptable. Your FSDO will make the authorization.
See also FAA RVSM Documentation