Here's another: tell him he'll be taking a backseat this year in terms of premium ice time, starting with significantly less PP time (Kakko takes his spot on PP1). Maybe he'll waive if the plan is made clear to him early in the offseason.
It will most likely hurt the team's maximum results to do this, but I'm not so sure this team doesn't need to withstand a step back next year before taking two steps forward. There's also a chance they become a better overall team as the year goes on. Even if Panarin stays, a 90 point Panarin and a 40 point Kakko combination is not as valuable as a 60 point Panarin and a confident 60 point Kakko, despite less combined points.