I would stick to raw veges. Along this line of thought though, you can scrape spaghetti squash into pasta/worm shapes and that tends to be pretty popular. Just be sure that it is chewed up well and the strands aren't too long. Butternut squash can be offered too. I've had good success offering it chopped into worm shapes, sliced thin with a peeler, or cooked and then worked into worm shapes by hand (this works with sweet potato too).