http://rvm.io/rvm/offline provides helpful instructions assuming you are starting with nothing. I already have several Ruby versions installed, so my process was reduced to:
$ curl -L http://www.mirrorservice.org/sites/ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.2-p320.tar.bz2 -o ruby-1.9.2-p320.tar.bz2 $ mv ruby-1.9.2-p320.tar.bz2 ~/.rvm/archives/ $ rvm install 1.9.2-p320 --disable-binary $ rvm use ruby-1.9.2 --default
Not too shabby! Many thanks to the RVM team.