Short answer is you can’t, not without a workaround. I brought this up yesterday as it’s on my wishlist for Dorico 5. (Request #17 here)
Longer answer is that once you are done writing/inputting you can do this by doubling the entire player, then use one player for the score layout and the other player for the part layout. Make each player look correct in the layouts to which they are assigned. It’s a pain, and if there are edits/revisions after rehearsal then you are stuck making the edits in two different places, but at least it can be done with a workaround.