Using local system-wide gems when using gem bundler

Gem bundle is a great tool, but I’m breaking my head here to try to solve what seems to be a simple issue.

Right now, we follow a very minimalist philosophy - if it is not needed, then don’t install it. For example, I use mongrel locally for development, while my co-worker uses unicorn.

In theory, gem bundle would include only the gems necessary for production, and any local gems would remain local and still available to Rails.

However, it does not seem to be the case. After I setup gem bundle (0.9.6, from source), Rails has been starting the server with Webrick, and it only used mongrel when I listed it in the Gemfile.

This is bad, because on production, this will install mongrel, which is not needed in this specific environment. I can think on other cases where I would want to have the gem locally but still available to Rails. Is it possible when using bundle?

Thanks in advance,