It should be easy to simply delete the notes in the piano roll editor which you don't want to send to the VSTi. I say "...it should be easy", not really know if it is or not in BIAB. But that is the way I do it in my DAW.

BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, 1TB WD Black NVMe SSD, 2TB WDC Blue SSD, 1TB WD Blue, 2 TB SK NVMe, 6 TB External, Motu Audio Express 6x6