I am not the programer but I am going wager that the answer would be NO. It would be great to be able to do that, then you could do an HTML block and design your header easier.
I think you are using the default theme, right. There are some great ready made themes on the SMF site and having tried almost all for my version of SMF, 2 RC 1.2, I have found several by one designer that captures the EZPortal forum button that are installed to the default theme. Also, the gallery button, staff, arcade etc if you have these installed as mods to your forum.
Let me know if you are interested in these and I will advise from my experience.
You can design a header in a photo editing program, upload it to your server, then in the current theme section of your admin, put in the URL of the header in the text box which asks for it and there is your header.