Thanks for the data. I have never looked at it that way. How about this technique if people still don't want to put the pumpkin in the boil (I don't)?
Before sparging gently mix it into the top of the grain bed. Let it sit for 10 minutes or so and then start then sparge, or mash-out, then sparge.
This way it should not plug up the filter, but the process of sparging should still extract the color and sugar from the pumpkin, and the 10 minute rest may even convert what little starches are there.