Bundler: `bundle package` with a :git source

问题

I'm trying to get my app to package my gems before deployment (to heroku) One of my gems in my Gemfile is a custom gem that I've written and I'm using the :git option of bundler to use the specific tag of my interest as such:

gem "my_gem", :git => "git@github.com:my_username/my_gem.git", :tag => "v0.1.0"

When I run bundle package however, this gem is not included into my vendor/cache directory. Is this a known issue, namely, that Bundler does not package gems that use the git source rather than a packaged .gem file?

I haven't found anything in the docs that says either way, but I was really hoping using this :git option would save me the hassle of having to actually build the gem and host it somewhere. (All this code is NOT open source or public in any way so I don't want to push it to gemcutter)

Also note that I need to package my gems first as heroku won't have access to the git source on deployment due to public key issues.