trick for faking ies effect:
i was searching for a tutorial about eevee and lights interior illumination and finally i found a trick that you (i guess) can import in rhino using enscape for faking ies light.
i used blender and eevee, but things are the same in rhino and i think enscape can replicate it in a good way.
add 3 source of light( 3 spotlights) at the same position, overlayed, or you can positionate them in different coordinate (such i made in my example) for all them you must chance the cone value, to achieve a light more sophisticated.
try by youself and post the result.
here my first attempt ( eevee like enscape for rhino, has not ies)
hope this was usefull, waithing for official feature