Load SpatialAnalyst in code

Does anyone have code showing how to check if SpatialAnalyst is loaded in ArcMap and if not, then to load it?

I have code that needs to have SpatialAnalyst loaded in ArcMap. I've figured out how to tell if my user has a SpatialAnalyst license and how to tell if SpatialAnalyst is loaded (via IJITExtensionManager.IsExtensionEnabled).

Now I want to load SpatialAnalyst if it is not loaded, but can't figure out how to do that.