If someone copied their data from the SD card to a computer, sent a legendary to a BW2 cartridge, and then recopied the data from the computer back onto the SD card, would that make it possible to transfer multiple legendaries? I don't know much about how the 3ds uses the SD cards, so my idea could be completely false.
You can back up tour memory card content on your PC, send the legendaries to 1 BW2 cart, restore the memory card content with your backed up data on your PC and send the legendaries to another BW2 cart.
Each Pokémon BW2 savefile can receive only one set of Legendaries.
3DS FC Ares 3738 0446 1787 <> Black FC Ares 0389 8392 9652 Dream World Collection: http://tinyurl.com/3qz7odk