First of all, I love, love, love the marble SSS you have going on. Nice work. 

CG is always a trade off of time and effort. I've put together a rough sample of a light cone and my stupid shader trick to imitate volumetric lighting. 

Carrara does not have volumetric lighting but it does have some volumetric effects like the light cone and 'god-rays'. So, my shader trick does a pretty good job of faking volumetric lighting but it would require you to composite in the background image/HDRI image to complete the picture. 

Compositing is how the game is played in the real-world so don't feel bad to do that. It has been suggested that you can do the haze/light rays in post production, and that is completely legitimate. However, I much prefer to have the software do as much as possible. Compositing in a background is much easier than re-touching in light effects. 

If you like the Shader Trick image, just let me know and I'll tell you how it's done. 

Mark