Is there a way to do this without duplicating the object? If I have a clear object like an ocean but I want it to have a uniform volume shader also. Is there a way to do this without duplicating the object and applying a water shader to one object and a uniform volume to the other?
The example I'm using specifically uses the principled shader with some solid and some transparent surface. I can't figure out how to have a volume shader inside the object.
There has to be a better way.

Yes, add the volume surface render property, and combine the surface and volume shaders with a switch based on the existence (non-zero) of dPdz.