According to the AIM Section 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](http://www.nbaa.org/ops/cns/rvsm/20140203-navigating-the-streamlined-rvsm-authorization-process-an-overview.php).  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](http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/rvsm/documentation/#docs_AIR)