I've created and maintained RVM::FW (with some help) for several years now. It works really well to make it possible to use RVM (or rbenv even) inside a restrictive LAN or Firewall.
$ git clone git://github.com/stevenhaddox/rvm_fw.git
$ bundle install
Create & modify config/rubies.yml or use the defaults in config/rubies.yml.example.
Download Rubiez and packages:
$ bundle exec rake boot:strap
Archive your local setup of RVM::FW and import it into your network.
RVM::FW is a simple Sinatra application so you can deploy it anywhere you have Ruby or Rack available internally!
View a demo to see RVM::FW's user views & instructions for how to setup and use RVM internally. Obviously there are no rubies due to file-size / RVM itself existing on the real Internet.
Ping me for feature requests/ideas (@stevenhaddox on Twitter or App.net) or Fork RVM::FW on GitHub to pitch in!
Bonus: If you're an rbenv fan but still stuck in a restricted environment you can use RVM::FW as a simple way to configure, download, and deploy a central location to keep your Ruby source code. Accessing your desired version of Ruby for rbenv is as simple as querying http://<yourhost>/public/rubies/<rubyplatform>/<rubyspecificpath>. All the Ruby source paths & packages are easily discoverable within the config/rubies.yml file.