How to turn cube into volume - on Vray GPU

[prepost_3d]

I have some ice cubes that I would like to add a spherical shaped volume inside of their center. Is there a way to do this all in shading? Or do I have to do this as an actual fog/vdb setup in Houdini? In Blender I can just simply add a volume scatter and then pipe a spherical ramp into it's density all in the shading network. Let me know if anyone has any suggestions! Also has to work with Vray GPU. (blender setup)
(current ice setup in V-ray)

[hsz]

volume scatter it just works in the CPU - so use VDBs if you want to work with GPU - Besides is fast and flexible.