Combine the pumpkin and the pumpkin pie spice in a large bowl, until well combined. Adding 1/2 C at a time, stirring well after each addition, repeat until you have added 1 1/2 C of corn starch to the pumpkin mixture. On a clean surface sprinkle 1/4 C corn starch, and knead the dough on this surface. The dough should be malleable, but not too sticky. You may need to add another 1/4 C corn starch bringing the total to 2 C, but only do so if the dough is still "sticky". Store in an airtight container in the refrigerator for up to 3 days. When removing to play with, let sit at room temperature for a few minutes before kneading. You may need to add 1-2 tablespoons of water while kneading to bring back any moisture lost while chilling in fridge.