Just a thought. You could print the WPF window to a BMP first and then convert to a PCL. That's how I would do it at least.
Here is some information of converting the WPF window to a BMP. Generating a screenshot of a WPF window
Here is some information on converting from a BMP to a PCL http://haykmanucharyan.net/Default.aspx?mode=2&id=33