New 4.6 UI: how to make UI elements cast shadows

im trying to get a few of the canvas’s and buttons that are rendered in world space, to cast shadows on the walls.
i can apply a material, in which case a panel can directly receive a light, but still doesnt cast shadows. [33136-bandicam+2014-09-30+14-38-28-908.jpg|33136]

The UI is still 2D even though it’s in world space. The best way to counter it not casting shadows is to place a thin cube or plane behind the UI.