Quote - killing the poser process seems a little extreme but that's all i know.

And it's the only one there is AFAIK as well.

The Render() method is sychronous (i.e. it doesn't return until the rendering process completes), so there is no opportunity to do anything to interrupt.
Even if there was a method you could call to abort a render, it would require you to be able to work with an extra thread within Poser Python and last time I checked, threads weren't behaving Pythonwise.