I am wondering if there is an API command that will allow me to schedule a broadcast into a conference?

I have tried the following:

sched_broadcast 5 UUID playback::tmp/test.wav

I have tried replacing the UUID with the conference UUID and no file plays (though the broadcast shows as being scheduled).  

I have also tried replacing UUID with one of the caller's UUID, the file does play but only to that one caller and not all callers.

many thanks

Matt