Instrument Doublings

It is very common for players to double on instruments in the same part, and there really needs to be a feature to allow that. Trumpet to flugelhorn isn't a problem since they are both Bb instruments. Only the playback sound will be off. However, going between two instruments of different transpositions and key signatures is a problem. I need to write flute (a non-transposing instrument) in a Bb tenor sax part (a transposing instrument).