In the case of Downloadable Content, you can load GDE data from a TextAsset like this:

// Adapted from Unity3D AssetBundle Docs
IEnumerator InitGDE()
{
  var payload = new WWW ("http://example.com/myBundle.unity3d");
  yield payload;

  TextAsset gde_data = payload.assetBundle.Load<TextAsset>("gde_data");

  if (!GDEDataManager.Init(gde_data)) {
    Debug.LogError("Error initializing!");
  }
}

If you encrypted your data with GDE, call the Init method like this:

GDEDataManager.Init(gde_data, true);