I need to get data from my Bing subscription into the MapnikRasterizer. At least that how I think it should be done.

It works of course in the preview because I made the Bing maps available through the options. But as I see it for the MapnikRasterizer I will have to provide the background as an image and I am struggeling to get the Bing data into my workflow.

How can I get the Bing data into the MapnikRasterizer?