Hi,
ok, haven't found a way to do it, so used a work around, as in the messenger script ( from the unify wiki), basically I create a gameObject and custom component doing the job, and integrate it in the action.
You can find that action in this post, downloading the microphone custom actions package:
http://hutonggames.com/playmakerforum/index.php?topic=1771.0Bye,
Jean