create shadows without a plane.

Hello everyone. I am working on a 360 project in Unity and incorporating 3D elements. I am trying to
create shadows on the ground (which obviously doesn't exist). Sooo... I'd like to know what would be the
best / correct way to go about it... here are my ideas..

1. Can I map my image as a spherical environment on a plane so it can receive shadows? (a bit like camera mapping in 3D software)
2. if not, is there a way to create a plane, but only to have it render the shadows and not the rest?

thx for your help.

Marc.