Hey, I think I've got an idea for the employer's devil fruit.
I call it the no-no Fruit!  I haven't figured out how it works exactly, but its ability is it allows for the user to "negate."  Basically it stops thinks from working like he can negate forces of nature, or turn off someone's devil fruit altogether.  Of course, the one thing I know for sure is he can't negate two things at once.