You can create a directory called /packages
in your project & then manually install each package and its dependencies. e.g for 'meteor router'
in /packages
git clone https://github.com/tmeasday/meteor-router.git
mv meteor-router router
git clone --recursive https://github.com/tmeasday/meteor-page-js-ie-support.git
mv meteor-page-js-ie-support page-js-ie-support
The second is a dependency on meteor router which you can see on the package's atmosphere page. It's recursive to make sure the submodule pages-js is also git cloned in.
Meteor 0.65+
As pointed out by thatjuan: Once you do this, you just need to add the main one to your project. You don't have to add the dependencies.
meteor add router
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