The NuGet PowerShell commands rely on being run from within Visual Studio so will not work outside in the normal PowerShell running from the command line.
You can however use migrate.exe which ships with the EntityFramework NuGet package and use that from the command line to update your database.
As a prototype I put together a way to use NuGet PowerShell commands from the normal PowerShell command line using SharpDevelop. Unfortunately at the moment the EntityFramework NuGet package does not work with SharpDevelop.
Another interesting project is StudioShell which provides a new DTE: drive inside Visual Studio but can also be used outside from the command line. I do not believe it supports NuGet PowerShell commands being run from the normal PowerShell command line.