RBlatter is a ruby script which allows you to add and subtract TeXmf subsets using the TeX Live TLPDB information.
This utility is likely run in place during packaging of TeX Live, but can now be handle as a gem too.
To install as a gem, run:
rake build
and the gem package should be in the ./pkg directory
Ideally, you will have the tarballs of the texlive bits (texlive-20130530-texmf.tar.xz and texlive-20130530-extra.tar.xz) and just run:
./mk_plist.sh
For usage of the rblatter command, read the mk_plist.sh and see the --help