Mix cup of soy milk with the 2 tablespoons of arrowroot and set aside.
Mix the soy creamer, remaining soy milk, brown sugar, pumpkin, and pumpkin pie spice together in a saucepan and bring to a boil. When the mixture has just started to boil, take off the heat and immediately stir in the arrowroot slurry. This should immediately cause the liquid to thicken (not a lot, but a noticeable amount; it will be thicker when it cools).
Stir in the vanilla.
Set the ice cream mixture aside to cool. Freeze according to your ice cream makers instructions.
Note: If you cook your own pumpkin, be sure to use a sugar pie pumpkin or other cooking pumpkin (not the Halloween variety).