The bad news is that, as of the time of writing, there is no way to edit the HTML header information in a Google site. And before I get blasted with comments saying that you can have a custom header no problem, please be aware: the header image and the header HTML are two separate and distinct parts of a website. Header image, no prob. Header code, no dice. Seems like Google wants to avoid me getting in there and breaking my website.
|Image: Wikimedia Commons|