And I want to subdivide the nonuplets into groups of three to aid readability. I don’t want to make it a nested tuplet, even if that is theoretically more correct it would clutter the part a lot more.
This would be very cumbersome to do manually in a large project, so is there a way to automate this?
AFAIK there is no setting that will automate this. However there are ways to make it less onerous. But you need to think about the best workflow upfront.