How do you add spoken lyrics in a specific rhythmic pattern but without pitch
Welcome to the forum, @Alastair_Russell!
I think you have to add a player for the speaker, and it depends how you want this to look in the score. From the “Sketch” family, you could add a treble staff, which would give you a 5-line staff, or percussion, which would give you a 1-line staff. Add notes with the rhythms you want (probably all on one pitch if you use a 5-line staff), maybe change the noteheads to X noteheads, and then add lyrics.
To keep those notes from playing back, you can either select all the notes in the staff in Write mode and turn on “Suppress playback” in the Properties panel, or you can mute the channel for the staff in Play mode.
I really just want to write what amounts to a rap: lyrics in a rhythm with no pitch. It appears at the end of a song where the same two singers have been singing pitched lyrics
Well, if you already have staves for the two singers, then you can try my suggestion, but leave out the first part, where you add a new player. Add notes with the rhythms you want, change the noteheads, add lyrics, and suppress playback.
The vocal scores for Hamilton and In the Heights both use five-line staves with x-noteheads on the center line of the staff for their rap sections.