I make premature endings by unfolding to one chorus and using a hold chord (example C...) as a last chord 4 to 6 bars before Biab makes an ending. You get a long naturally decaying part on all but a drum crash. For the drum crash I go to the folder (BB > Drums)there's the drum files and there are single parts along with the drum beats and I copy and paste them at the end. Usually save the drum hits for future use too.