Try slowing the simulaton speed down to like 50. It seems very slow but it will teach you how to do them really fast. Then once you can do it relatively well start increasing the simulation speed. The major thing that will help you is doing slow rolls/rolling circles. I also spend a lot time with just a radio practicing the inputs This helps a lot. The yak-54 is the best plane in that game for this kind of stuff. I could make some recordings of rolling harriers for you if you would like.
Joe