I'm not sure BIAB can do this, and it is indeed a useful function. I normally do that task in a notation program where I highlight all the notes except the lead (upper) line and delete them all in one action. Doing this on each staff eliminates a lot of the individual note deletions otherwise necessary.

I know some also do this task in a piano roll editor. You can highlight a range of notes and blow away large amounts of the lower notes.

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.