Hi, I already did something like this before but I totally forgot how…: the second voice ending in ‘hidden’ measures in the middle of a staff…
Anyone knows a fast solution for this? THANKS!
Apologies if I misunderstand your intentions, as it depends on why you have that voice in the first place. I don’t want to give a non-answer, so I’m starting by saying that selecting the measures you want to delete, right click, select “Staff => Manual Visibility. Enable manual visibility in the dialog that comes up for the staff in question, and then select hide.” That is the brute force way with lots of things possible. Of course right clicking, ,menus or key commands - you choice. … BUT ALL THIS AS A LAST RESORT 
An Ossisa staff might be better, and you’d select the measures where you WANT the staff, right click and go "staff => create Ossisa Staff. There is also something similar when parts divide of inserting a divis tag where it begins, and a unis tag where you want them to come together.
You can add extra staves for a player which can start/end in the middle of the system.
However, if you mean II to be an entirely separate player and you’re looking for “cut-out scores”, Dorico doesn’t currently support that easily I’m afraid.
Manual visibility: not helpful because this applies to whole system. I would really like to have it on the same system as a hidden measure.
An ossia staff could work.
An extra stave is maybe even better…
But as I think I understand well: it’s not really supported yet.
Thanks for your replies @Lillie_Harris and @gdball !