With 2 instances of BB you can copy from the audio track to audio track.
You need to save the track as Performance and move it to the audio track, copy the section of track you like to the other audio track and so on.
You can save a master stereo wav of your song, load it in the second instance audio track, generate up 7 of the same instrument, solo track 1 and the audio track if there is a section you like make a note of it, now solo track 2 and the audio track and make a note of any sections you like.
Now you can save track 1 as a Performance and move to audio track replacing the song master, now with "Snap" on copy the section you like to the audio track with "Snap" on in the first instance and so on.