I think you can use it with the parameter BuildOptions.BuildAdditionalStreamedScenes to create asset bundles that can be loaded dynamically by your game. But BuildPipeline.BuildPlayer is an editor class and can only be used in the Unity editor. You can create an editor script that allows you to build only a special level as own asset bundle which can be loaded by your game using www.
I've never used assetbundles so i can't tell you more about that but that's how it should work. Maybe we get another answer from a "asset bundle user".