The answer depends on which version of Invigorator you're using. For example, Invig Pro AE 4 and ProAnimator 4 include a torus primative. One click and instant donut. Without a primative, you could create a custom edge bevel.. I haven't tried it but a circle offset from the centerline axis in the Illustrator docuument, applied to a small sphere in Invigorator should work.
Adding the icing and sprinkles could be done with a bump map and a texture map, or you could go to the trouble of actually creating and placing individual 3d sprinkles... if you're getting so close to the donut the illusion from the bump map would be lost... and if you've got lots of time.