Gunpowder.
NO! Just kidding. But I have been sorely tempted.
Fill the hollow rotor with grease, then with a close fitting rod and a big effing hammer proceed to drive the two apart.
You will have to be creative as to how to fill the rotor with grease, you will have to start at the bottom of the hole, of course, and watch out for air bubbles, they will cushion the blows from the hammer. A steel line of the appropriate size and a drive in grease fitting works pretty good to fill from a grease gun, or you can adapt with various fittings and unions.
I wish you luck!
Ron.