Let the straw hats kidnap Greenbull and use him as leverage for whatever transpired at the Reverie.
I think it'd be better if he took a risk with the straw hats outside the ones he's always using.
He takes risk with side characters, gives them an enormous amount of screentime and development even when popularity polls come out and show they don't even rank in the top 60 but with the straw hats ....
If they aren't Sanji, Zoro, or Luffy they'll just get a two-three chapter plot line then back to the background they go