Yes, and it is even documented on https://getcomposer.org/doc/05-repositories.md#disabling-packagist-org
You may try to use this command:
$ composer config repositories.packagist false
You probably want to have a look at Satis: http://getcomposer.org/doc/articles/handling-private-packages-with-satis.md
It will make your life easier if you deal with a bit more of local/private packages, because otherwise you'd have to mention EVERY repository that might host required code. And you can use Satis to grab a copy of the versions into a ZIP file that can be hosted locally as well. See http://www.naderman.de/slippy/src/?file=2012-11-22-You-Thought-Composer-Couldnt-Do-That.html#13 for some hints of how to do it (press cursor keys left/right to skip through the presentation)
For extra bonus points, you'd add packagist.org as a Composer repository to Satis, require some needed packages, and set { "require-dependencies": true }
to grab their dependencies as well. In your own code, you'd only set your Satis repository and disable Packagist.