You could try inserting a Transparent Caption with no text,
then assign a mouse click sound to the caption so that when it
appears, the sound plays. But I have a nagging suspicion that this
has an issue. Seems I recall that there are audio issues with
Transparent Caption types. But still try it. Maybe I'm off in what
I'm remembering. Admittedly, this would require a bit of trial and
error in order to get the timing to match when the click occurs.
If that were to fail in some way, perhaps create a tiny image
and insert that. One that wouldn't be noticed and placed in an
obscure location. And as earlier suggested, attach the sound to it
and time it to appear when needed.
Hopefully this helped either directly, or spawned a thought
that does work for you.