The best way to do that is to use several steps in your recording process.

I'm not sure that BB can actually do that internally at this point.... it's one chord per beat with 4 beats to the measure. You're needing eighth note resolution and that's not a feature....yet.

The steps mentioned would be to create in BB and then move to the DAW to do the audio editing as needed using the tools available.

If you take the project into a DAW of some sort, you can edit the places where you need 2 chords to a quarter note beat using eighth note resolution and/or, use MIDI to get you there.

If I was to do that, that's how I would approach it.

Others may have other solutions.

You can find my music at:
www.herbhartley.com
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The magic you are looking for is in the work you are avoiding.