load scene without lag

What is the best way to load object into current scene without lag? I try to use LoadLevelAdditive, but when I load a new scene the current scene stop until the new scene is load. If I try with prefabs?

You can use LoadLevelAdditiveAsync, but you need to own a Pro license.

Edit

LoadLevelAdditiveAsync loads a new level on another thread,
but when you only need to load single objects, I would suggest instantiating prefabs.

You can simple put in your code:

C# example

GameObject newCube = GameObject.Instantiate(cubePrefab) as GameObject;