Hmm, now where did I put that plot bunny fertilizer? I know I had it around here somewhere.

You know, Cloud could hear about and/or learn the Dragon Slave and realize when he gets back to Gaia it doesn't work.

So what does he do? He immediately starts looking for a new source of power to power something akin to the Dragon Slave. He then sees either Bahamat Zero or KotR being used, and is bound and determined to pull their power to use for a new Dragon Slave-esqe move.

Or hell, since Jenova is the evil badguy type thing, maybe abuse it's power to make the spell?