I have made songs that had leads played in different keys, but only in a Relative Minor. I entered the song chords and made wave files, then rewrote the chords and generated a solo and brought the tracks into my DAW. That is the only way that I found would work for me so far. I had planned to try Mixolydian to force a flatted 7th,but haven't yet since they have Bluesy versions of some leads now. It would be a great wishlist item to post, "Mode Button".