I find if you have the pumpkin off and just poke the splines into the driveshaft it will engage quite easily into the shaft, I have done it that way several times.
Rock the rear wheel back and forth, it will just slip in, at least mine does, I usually find at least one of thee cush drive rubbers fall out, leave the rear brake support brakets out initially and you can push the rear wheel over enough to work the cush drive back together.