Hopefully, we can figure something out so that the CLI, the web console, and the underlying API all match up a little better. But it's complicated, especially because of the traditional meanings of terms like deploy and undeploy.
Anyway, this functionality now exists in the latest web console. So if you grab a nightly build of AS7 or wait a few days for the CR release then you will have an easy way to do it with a nice web UI.
So back to your question about using the CLI. Once you have your deployment uploaded to the content store, the command to assign to a server group looks something like this:
/server-group=mygroup/deployment=foo.war/:add
Then, to enable the deployment so it will actually deploy, do this:
/server-group=mygroup/deployment=foo.war/:deploy
Stan