Keyboard player here. Been there, done that. And I hear a lot of what's already been said in this thread. His changing will be difficult. I've played for years with a guitar player who learns songs not guitar parts. So he plays the intro to Cream - Badge and the organ line in Talking Heads (version) - Take Me to the River and so on. Nothing anyone says changes that. Or more simply, have you ever known a guitar player who can play 'Tacit?' Rare, that one.
Over twenty years ago when I got back into playing, I took a lesson from a respected local jazz cat. First thing he criticized, "You have a bass player. Why are you playing all that poopie down there?" His constructive suggestion was to learn to build my voicing off of the third or seventh (blues) or other chord tones other then the root. It took a year of work before I could do so fluently. Now my keyboard playing sounds more "out there" when it's really not. The only issue I found with that is when I am playing with what I call the, "Lead Bass Player."