User blog comment:FairyRaven/Fairy Tail Chapter 360:The White Inheritance, Review and Commentary/@comment-24066070-20131115194948/@comment-24066070-20131115213041

Ah yeah I forgot about that limitation. But indeed if Jackal is tired or Gemini has gotten stronger somehow, it might work.

Even if copying Jackal doesn't work, she may try to copy herself and cast Urano Metria for real this time, although some other Spirits or Wendy would have to keep Jackal busy during the incantation.