audible metronome in MIDI file?

[Jimmy Wilkinson]

I’d like to hear a metronome in the MIDI file generated by Lilypond. The best 
thing I can think of is to add a new voice that plays some high short note at 
the beginning of each beat. I’m hoping that there’s a better (easier?) way that 
I haven’t found.  It’d be nice if I could just ask Lilypond to do that and have 
it affect only the MIDI file and not show in the printed score.

thanks