Casting shadows on pre-rendered background

So the game is a side scroller, and i have a pre-rendered background, the thing is i want the character to bump into and cast shadows on the foreground space.

So for example, if we imagine the image above as being both the foreground and background, i would like the flying character to simply collide with the car and cast a basic shadow on the ground and on top of the car (so that it looks like its in the space).
i was thinking about making the foreground objects in 3d, but i want to know if it is possible this way first.

maybe create an invisible collision object for the car (in this example).

and i have no clue as to how im going to do the shadow.