Advice on adding text between arias

What is the best way of adding blocks of spoken text between arias in an opera if I want the text to appear in the conductor’s score and the vocal score (both in different formats) but not in the instrumental parts?

I’d use a custom Flow Heading that has a text block above the title. Then you can put the text contents in “Other Information” or similar for the flow. You’ll have a Flow Heading Change, but not a Page Override.