This supports simplified loading buildpacks from a private git repository / repositories.
It hooks in only to the compile stage of each buildpack.
Requires custom-ssh-key-buildpack or similar.
Add .heroku-private-buildpacks file in the project root:
git@github.com:user1/private-repo1 git@github.com:user2/private-repo2 # ...