We currently have a c++ plugin that whe are trying to port to CS5 using AS and CS Extension Builder. In the plugin, I intercepted the export of the PDF and by using the IID_IMETADATACCESS interface on the document, I could insert a new xmp namespace with serveral values needed inside the metadata report in the generated PDF.
We want to do the same configuration in the new extension. Is there a way to create a new namespace in the metadata packet and insert my list of needed values?
This question might get more traction in the InDesign scripting forums. In general, if you can do it with ExtendScript, you should be able to do it with ActionScript. Also, you might want to look into the InDesign Host Adapters which allows you to get the XMP from a document, here's a recent question on the topic: http://forums.adobe.com/message/4008254.
Does that help any?