You mute the track where a riff ends then generate the next track to play from there this will work the same way that BB generates a whole track.
If track 1 plays good until bar 19 you F5 mute @ 19 and freeze it
now you can leave track 1 soloed (and the Audio track) now solo track 2 as well,
track 2 will be F5 mute @ 1 so now we F5 back to normal @ 19
hit play generate until we get it to flow and fit from track 1 bar 18 to track 2 bar 19 and on until a good section of playing ends and a bad bit starts, then mute, freeze, track 3 F5 back to normal... and so on.
Track 1 maybe give you good playing in the first and last chorus but the middle don't fit so you just generate the middle on track 2.
ReaTrak Integrate Biab & Plugin in Reaper
Free Biab & BiabVST Chord Picker Tool