Unity3d - Cast dynamic shadows without processing multiple lights

Question

Back Story

I've built a game with a friend and all goes well until there are too many spheres under a group of 5 lights, then things start getting choppy.

Troubleshooting

I've found that by turning off all of these lights but one the game runs smoothly, the problem is that the shadows are not realistic at all. Because of the 4 main lights, the objects should have four main shadows.

My Ideas

I wanted to use a "projector" but that is too static for multiple & random appearing / disappearing objects. I might be able to do a projector per sphere but I'm hoping there is an easier way as this would require a lot of work to get just right.

Question

How can I get 4 lights to cast a raycast shadow on a group of dynamically moving spheres (100 of them) without processing the light portion?

Answer 1

We got rid of the four extra lights and instead attached projectors to the items. The projectors shoot black, circular png shapes onto the ground. It took a bit to soften up the shadows / lock rotation etc but it came out nicely and we saved the performance that we needed to.