Preview-Output to more than just Monitors OR Headphones

I would love to be able to get the preview not only to my main-output or my phones alternatively, but to all cues & monitors I want it to be heard on. It would be great to playback some preview audio to a singer in the booth for example (to give them a solo bit of their pre-recorded tracks for doubling, to to teach them a harmony previously recorded by another singer. Also would be handy when using more than one headphone while mixing.
A switch like the one determining where the click should go would also be great to have for the preview sound.