File_PDF background images

Hello, I have been trying with very little luck to insert a background image into a PDF document with File_PDF. Since I don't know pretty much anything about how to create a PDF document from scratch, I have been at a loss as to how one might overload one of the existing File_PDF methods or create one from scratch to write the image as a background image to the document. I have done a significant amount of looking online to try to find an answer, but it doesn't seem like many people are talking about background images and those that are don't have a usable PHP-related solution. My questions are 1) is there a way to do this with the existing File_PDF and 2) if there isn't, is it something I should request as a feature request. I would put it in as a feature request, but as I'm not sure that this is possible with PDF, I figured I'd better ask first. Any information would be greatly appreciated. Thanks.