The King Punch requires Elizabello's special body type. That's what I would assume.
The only thing close to that with Luffy was his Boundman form which does have its own signature punch. Kong Gun.
Although, in Nika form, he can buff up, and that could allow him to translate his body into the type needed for the King Punch, I'm not sure if he can do the same build-up that he does. Elizabello spends a long time charging that thing.