Option to create duet/multi vocal songs

[Baklap4]

I'd love to have an option to create a duet song (2 or more vocals (see performous/performous#235)) with composer.
Currently the only option to do this is by starting a new project, and create a txt specific for the 2nd or 3rd singer. Then copying those lines back into the original one and add the tags P1, P2 (and in the future maybe PX where X is equal to the amount of mics we have connected)