I have a JAP spec Zed, with no rear fog light section, my solution was to convert the reversing light (“Backup lights”) section so that it was a dual purpose reverse and fog. I added two extra bulb holders and made it so the bottom two are still reverse and the top two are fog. I also used LED bulbs in all.
My understanding of the OP was for a better reverse (backup) light brightness rather than rear fog lights. Cheers.