Since you want more movement from the bass (not just main notes), there are some alternatives. A bit more work, but certainly do-able...

One way would be to begin by creating your BIAB file (SGU) with your chosen chord (Bb for example) as the only chord in the verse and your other chord in the chorus (Ex. Eb) and generate the bass track and FREEZE it.
Then, continue to input the rest of your chords for the song for your other instruments to play.

The other way would be to make a separate SGU - with those two chords (if you did not want to start over to do the Freeze thing). Again, just use your 2 Bass notes and export the audio. You can then import that into you other BIAB file as an audio track.
I believe that if you name it properly (I do not know what that name IS, but others can probably tell you - Charlie Fogle or Noel Adams would likely know), and put it in the same folder as you full SGU, it will automatically load it to the Bass track...


150+ Songs produced using BIAB RealTracks
And 50 more...
and some more...