"Sibelius seems to have a similar problem - you can't write a section that starts with an upbeat and ends with a matching incomplete bar"

If you're writing directly to Sibelius you can.

When you set-up the first page it asks you if you want to start with a pick up bar and you can define its length. The irregular length bar at the end of the section is then created by adding a bar from the 'Home' task bar.

Repeats can be added from the 'Notation' task bar and you can also repeat any bar as many times as you want from 'Repeats' on the 'Play' task bar.

Greenie