Bahamut.Eythan said:
If you are a higher level go to Abyssea and cast debuffs on worms. Sub Whm and either cast silence on them so they don't use magic, or just sleep them while they are casting.
I was seeing 15-20 levels on both string and wind in less than an hour.
As long as you don't requiem them you should be able to just keep them slept and keep spamming threnody.