Okay, well, in case anyone else needs to know how to do this, I have figured it out and here is how it's done.
You have to modify two files:
Add your image CSS to template.css
Then add the class information to yjsg_headerblock.php as a div like this.
If should go right after the header ID line:
<div id="header" style="height:<?php echo $logo_height?>;">