HeiPet, I see that Daniel and I have interpreted your original post in different ways.
Daniel’s assumed that you’re using the same voices (players) for the chorales as for the longer movements. I’ve assumed that you’re using different voices (players).
If you go down the route of using one set of players for the longer movements, and a different set of players for the chorales, then there’s no need to do custom layout work in Engrave mode or fiddle with frame chains. You can just set each of your flows to contain the correct players (following the instructions I gave above), and then set each of your part layouts to include the chorale players (by right clicking on each layout, in Setup mode, in the right panel, and ticking the chorale players).