You can try using the light object with a blank graphic, then create a sprite at the centre of the light object with the image you want (and decrease it's opacity).
The shadows should still cast (the light range isn't dictated by the graphic I think)
The light object's graphic itself is required to handle multi-level shadows on a single layer such as in this example:
You can do single-level shadows in that exact way though, but that's not what we're looking at. Besides creating objects dynamically would still require differentiation through private values in our implementation.