According to the documentation you can add a project from the registry or from a tarball url?
# add plugin from plugin registry
meteor add cordova:org.apache.cor
You can no longer add a Cordova plugin with a tarball URL (I'm using Meteor 1.2.0.1) and there seems to be some sort of bug using the hash value as the docs recommend. Here's what I did instead:
First, I cloned the git project under myapp/private folder. It's important it's private otherwise Meteor will pick-up the www/*.js files and try to compile like normal causing other issues (e.g., "module" or "require" is not defined).
Second, use the following command to add them to your project:
meteor add cordova:com.loutilities.qaps.mobile.plugin.phone@file://./private/plugins/cordova-plugin-phone
This will them to the cordova-plugins directory along with the other bits they add.