Just thinking - you COULD produce a KARAOKE file of an unaccompanied song. You would just assign the words to rests instead of notes. Of course, the singer would have to keep to the tempo of the file.

BTW
It is not clear whether abc officially allows aligned lyrics on rests. Some software packages allow it (including HARMONY) , and some don't. If not, then you would have to put notes in , and mute them on playback. This can probably be done by sequencers, and the resulting file saved.