Just seen this otherwise I’d have replied sooner! I rather disappointedly found the same thing, no tail lights in the 7mm version yet they managed to squeeze both front marker and tail lights into the 4mm one...
Anyway, I wanted tails in there as well but without having to do lots of making up of new light units. I solved it by fitting Some dual red/white DCC concepts LEDs glued into the same loactaion as the original ones. Although they are effectively 2 LEDs glued back to back, the rearmost LED reflects plenty of light back onto the light lens.