Testing to see if it's feasible to trim down a repo with the goal of submoduling.
git clone https://github.com/twitter/bootstrap.git
rm -rf <directories and files you don't care about>
git commit -am 'Trimming things out'
On github: create an empty repo, say docless_bootstrap
git remote add docless <r+w url>
git push docless master
Now the docless repo can be submoduled into another project:
git submodule add <docless_url> <local_path
(Further reading: http://git-scm.com/book/en/Git-Tools-Submodules)