Check out Peter Cooper’s article about speeding up ruby’s load time (require code) without going to edge ruby (1.9.3).
TL;DR
$ curl https://raw.github.com/gist/1008945/7532898172cd9f03b4c0d0db145bc2440dcbb2f6/load.patch > /tmp/load.patch
$ rvm get head
$ rvm reload
$ rvm install ruby-1.9.2-p180 --patch /tmp/load.patch -n patched
$ rvm use ruby-1.9.2-p180-patched