Here is something I have been doing lately during practice. I found a key ring that is almost the diameter of the bull and I suspended it over the T20 using a pin and a length of thread. If you zoom in on the picture you can make out both the pin and the thread. I think this is helping me with T20 practice but I am not sure yet. The idea is that when throwing at the bull I reasonably expect to hit it. I have a lot of confidence and decent grouping when I am doing bull practice, but my T20 throwing suffers quite a bit. So I decided to try to simulate the bull throwing mentality a bit for the T20. The picture below is an actual practice round. A good one for me. The third dart was so far off though, that it could not be included in the picture. Now when I practice T20's, I go for the ring and ignore the actual triple.
As always, click the image for a larger picture.