perhaps you can include a "empedded_image.tpl" in pagelayout.tpl. Depending on the class identifier you can use the override system to include different templates. I think this should work even at this level.
As far as I know, template inclusion would slow down eZ Publish. Or has this problem been solved already?
In my case, virtually every class using the standard pagelayout.tpl should be able to override the header image, so the template inclusion wouldn't be a benefit for me.
Maybe I should try the other way around and integrate the navigation into the content view templates. That way, there is no need to do a seperate fetch in pagelayout.tpl.