I believe in the current lumen implementation that it’s very difficult to impossible outside of screen-space. There’s no easy representation for the lumen scene to reflect water color correctly, especially considering how SingleLayerWater is made up of a lot of shader tricks and isn’t as physically based as other parts of the engine (laymen’s terms).
Theoretically, you could represent the ocean in software RT like this: Use the water height to drive a heightfield representation in the lumen scene (just like how landscapes are represented), with stochastic translucency to account for light partly reflecting off of and scattering into the water. That may even be something a tech artist could set up without programmer intervention, but it would certainly be a hack.
I don’t see an easy way to do anything for HWRT though: the densely, dynamically tesselating surface with constant movement would likely have massive BLAS update costs under the current lumen paradigm.