I figured out how to fake the rest symbols with a different notehead set, but it seems it’s not possible to show any rests in these incipits because Dorico tries to line up the rhythms. Any long rests at the beginning such as the ones below push the subsequent notes too far. Here’s an example from Lilypond where rhythm is completely ignored in horizontal spacing:
Any spacing hacks or other ways to replicate this that I’m missing? (This also shows an example of double B-flats.)