To control LEDs using a spare servo channel, I prefer one of these from Pololu:
http://www.pololu.com/catalog/product/1210
http://www.pololu.com/catalog/product/1211
I didn't want to use the dji provided mast either. Apparently it is to prevent interference due to RFI.. so I just made a small enclosure and lined it with copper tape to shield out RFI: