I have always called this by getting 987 in position first, then 654, and finally 321. Then I tend to just reverse it. My daughter Charlie called it last week and she moved just one bell in each group then did the same in the next group and the next, so b to c in each group of three, then a to c in each group, then a to b. Which just shows that if you think about things with a fresh mind it can be quite different.
Care needs to be taken to ring Rollercoaster well! In particular, 6 must be close to 1, and 9 close to 4. Too often the bigger bells are slow over the smaller ones, causing the row to separate into three groups of three bells.