I think they're talking about using a rayswitch shader in the camera's environment slot instead of the physical sky, then plugging your sky map into the refraction/reflection channels of the rayswtich and the physical sky node into the final gather and any other relevant slots needed to preserve the lighting. This method is similar to one of the ways I tried to add clouds to the physical sky. I ended up creating this as my workaround. And here is another article going through other ways by someone else.