I'm actually not that crazy about the script you linked; I've seen it used in conjunction with other form platforms and its support is spotty. What I would recommend is to use Modernizr instead, which adds several other types of backwards compatibility with forms. You can either customize the script or just use cdnjs' version, which has everything included.
Forms 2.0 placeholders already are polyfilled for IE9, AFAIK (even in IE8). Obvs. they don't use literal placeholders but then no library can do that, either. What are the exact issues, and why not attempt to solve them using the existing functionality (the fonts can be a little wonky, for example, but that is easier to fix using CSS than to add an entire library).