As a complement to @Casper's answer:
I created a directory for my Gem system files.
Then I added a directory for each version of ruby. I wanted to install system gems. I added a Gemfile to every directory and .ruby version file with the correct version. Now I can install the system stones for the ruby โโversion using:
$ cd path/to/system_gems_dir/1.9.3-p484 $ bundle install --system
or
$ cd cd path/to/system_gems_dir/2.0.0-p353 $ bundle install --system
source share