It would be great! but maybe it's a technical issue if it hasn't bee done yet ??
As the tracks are actually in RAM.
If you could select a section on the chord sheet, right click copy Bass,
then in another instance, right click paste Bass and this will copy and paste the same RT section data as the SGU saves frozen track to.
Then all you would do is regen that track using the existing data plus the new section data to a new track in RAM.

But yes, you could load the Biab Plugin into BB, if you just had the drag n drop import into the Audio Edit window and also for midi in the piano roll.
You can use the Biab Plugin in BB to generate a small section with different chords to preview the master or separate tracks, just load the Biab FX Plugin on the Audio track and solo it then hit play in BB.
C:\bb\BBPlugin\Files\Band-in-a-Box DAW VST FX Plugin.dll


Also:
Biab32/64 MultiRiffs with EnergyXT2.6 Win