No luck so far. I've done the following, which clears an error about the incorrect light switch and causes the icon on the instrument cluster to work.
BDC_BODY2 (Mine had 4 CAFD entries, the sections below were in the last one for me.)
3070 LceConfiguration > Funktionen > LCE_BEL_LIN_VAR
Changed from 39_BEL_PL_FLC_NSW_NIVI to 40_BEL_PL_FLC_NSW_NSL_NIVI
(You'll basically want to change the default value to the same thing but with NSL added.)
3075 LceMaster > Funktionen > NSL_Verbaut
Changed from nicht_verbaut to verbaut
It seems like the other settings for this should also be in BDC_BODY2 as the taillights connect directly to that module if I understand BMWTIS correctly. (Diagram
here for my 540d) I did verify that I have the rear fog wire running into my taillights and I see LED diodes in what I think are the rear fogs so presumably it really is just some extra coding. I tried changing a few NSL-related things but no luck.
So... half way there?