Combining raymarching objects with regular geometry

Hi!

I want to do exactly what is written here:

Unfortunately, I have no idea how to start this in UE4. I have raymarched geometry, some basic cubes and spheres (Custom Material Node: How to use and create Metaballs | Live Training | Unreal Engine - YouTube). I have to place real geometry inside the box I raymarch in and I would like to have proper depth for regular and raymarched objects.

Golden rectangular is raymarched inside the cube. Although landscape is above rectangular, landscape does not cover it, which is incorrect.