You cannot achieve this with slide audio, but if you attach that audio to an 'invisible' object (perhaps a rectangle with transparent fill and no stroke) you can control the audio using advanced actions to show/hide that object. That is the way I realized several effects in my latest blog post. If I want control over audio I will never insert it as slide audio.
So the work flow would be to hide the animation with its attached sound and show the invisible object that now plays the previous slide audio. When the user click to view an animation, attach an action to this click box (or button) that hides the invisible object and shows the animation.
I did this and it works.
Thanks a lot, this is a nice workaround !
I love the control that object audio is offering, once you get the hang of it, and it took me a while