In the Crysis 2 editor, do the following:
-Go to the console (you can find it in the top menu in View > Show Console) and type this in: r_pointslightshafts 1
-Now put a light in the scene and in its properties you will see one called "PostEffect", change it from 0 to 1.
There you go!
If you want something more permanent, you can make a flowgraph that sets that cvar at the beginning of your level by using the Debug:ExecuteString node.
edit: added images.