Bit of a long winded process, but you can do the below which may help:
Place the photo onto a floor plan
Open the 3D View, go to the View Menu > 3D View Options > 3D Styles, set the 3D Engine from OpenGL to Vectorial Hatching and close the dialog
Navigate to the View Menu > 3D View Options > 3D Projections click the parallel projections button and set your camera to a top down view, set the sun to the desired position and click OK
With the marquee tool draw around the model and then press CTRL+C a dialog will appear asking what you want to copy, in my case I selected just shadows (Edges and Polygons) also ensure that it's set to scaled drawing at the top:
Go back to floorplan and paste it (CTRL+V) and the shadows will appear something like this:
The elements that are pasted are fills which you can modify the colour of if you wish.