Matt is right on track. I do this all the time. However I am using the midi file as is and merely muting the tracks (instruments)that I am going to play. (Keyboard and left hand bass) Open the midi file in BB. Do not use import midi file. Then click on the green SeQ icon and choose seq on Melody tracks. Mute the tracks you don't want. In the seq make sure you have Custom channels/tracks play selected. You can use BB to change the key as well.