Hi Paul,
It is "possible" to be able to write your own extensions to any Java API available on the BlackBerry and make it available to your widget. This would allow you to accomplish what you are looking for.
We don't have much published information on how to do this yet since we are trying to make a nice "supported" way of doing it through our tooling. But you can write your own extension in Java that exposes your own API in JavaScript and modify our widget template code to add your functionality when your widget is packaged.
We will be having a session on how to do exactly this at the BlackBerry Developer Conference coming up next week. We will likely also try and publish a tutorial after the conference as well showing how this can be accomplished.
Your suggestion is a good idea for a new Widget API, so I will put it on our list of new API's to deliver.
