This HOWTO is based on the RVM page http://rvm.beginrescueend.com/deployment/system-wide/. But I find the RVM site documentation makes a few assumptions with regard to commands.
1: Install git if you don't already have it
2: Download RVM
$ sudo apt-get install git-core
This creates /usr/local/rvm and the group 'rvm'
$ sudo bash < <( curl -L http://bit.ly/rvm-install-system-wide )
3: Add each user to group rvm
4: Add startup lines to each user's .profile
$ sudo usermod -aG rvm ubuntu
5: Add this line to /etc/rvmrc (may not be necessary)
[[ -s '/usr/local/lib/rvm' ]] && source '/usr/local/lib/rvm'
6: Use rvm as a user - best to logout/login first to make sure you get all the paths etc setup
$ echo "export rvm_path=/usr/local/rvm" > /etc/rvmrc
Note that you use rvm as a regular user, not via sudo, even though this is a system wide install.
$ rvm list
$ rvm package install zlib ( I needed this to get install to work )
$ rvm install 1.9.2 --with-zlib-dir=/usr/local/rvm/usr