This can only be done using the 2D editor. for starters, try shifting the box in the 2d editor to the side of the middle point leaving like 128 units between the box and middle. Now hit the button atop that window (sorry ' forgot the name of the button, am away from my ued. It's not the extrude buttons or the sheet button, but the other one) close the window and see the result. Now try doing the same leaving 256 units (instead of 128) of space between the box and the middle point and see the result. This should get you started. Then try resizing the brush in the 2d window and try it again. You can choose to make a complete doughnut, or just a piece of it.