Extracting GameObject from scene package

I have a scene in Unity that is exported as a package using the following code:

 string outputPath = sceneName + ".unity3d";
 string result = BuildPipeline.BuildPlayer(new[] { inputPath }, outputPath,
     BuildTarget.StandaloneWindows, 
     BuildOptions.BuildAdditionalStreamedScenes);

When I load the package during runtime, I use a WWW like this:

 var www = new WWW(packageUrl);
 var ab = www.assetBundle;
 Application.LoadLevel(sceneName);

I want to retrieve the terrain from the scene. In Unity, the terrain is just called "island_terrain" and is part of the scene which is packaged above. How would I go about getting the terrain GameObject/Component?