Well, I do "troll" around here occasionally, so not much harm is done if the question is asked here, though it definitely gets my attention faster on the official support forum (that is free too, FYI).
To answer this particular question I believe the solution lies in the site setup (and that is not necessarily dependent on the theme). If this is a "sub-site", is the sub-site a specific sub-domain on the main site? If so, is this a multi-site installation? In case of multi-site installations the solution is really simple - the theme can be customized for each site individually. So you can have a different header specified in the options for your sub-site.
If this is NOT a multi-site installation, the solution is still quite easy. Basically you need to set a header specific to certain pages. If you look at the source HTML for your pages you will see that the
body HTML element gets a class specific to the page. So the header for that page can be determined by using the page class and the header id together, and defining a CSS rule in Suffusion Options → Back-end Settings → Custom Includes → Custom Styles should do the trick (I am assuming you are not using a child theme).