Sure, you can construct a shape out of CollisionPolygons. You can load such a shape out of an egg file, for instance with the { barrier } tag. Search the comments and/or the manual for more information.
Note, though, that the more polygons you have, the more inefficient the collision test will be. Ideally, the torus you construct for collision detection will be much blockier than the one you would construct for rendering.
David