Hi René,
I haven't tried this but below is something that might give some bluesy notes ...
Enter into the Melodist and then select the "Edit" button.

In the right column of the Edit dialogue box is an option to have a melody created around a "Mix of minor and major progressions".

By default, the weighting for mixing major/minor progressions is zero. Try setting this option to (say) 20 or 30 and see what happens.
Introducing the potential for minor key notes should mean that flattened 3rd, flattened 6th and flattened 7th notes become available for making the melody. The weighting will determine how often this happens (the higher weighting, the greater the likelihood it will happen). While the b6 note will have limited use, and may or may not need editing, the b3 and b7 notes are useful blues notes.
I have no idea if this will work but, in theory, it sounds like it should.
Regards,
Noel
P.S. If I did need to edit any of the notes, I'd be using the Piano Roll mode since it's much easier to modify pitch and duration with this.