Keen on this idea also, maybe integrated into the HTML Widget in Extend > Widget as a 'only show on category no#' would be totally sweet, as I don't think you can do that on that widget yet, but on some of the Widgets you can (i think).
You could stuff anything in it then and have it appear on individual pages
@Guiri - Custom Header is just for changing the background-image's in whatever css div/class you specify in it's ACP config
not really used for implanting code, but I guess you could use it that way , with a banner (?) just use a HTML Widget and create a css class="someclass" for it, then put that in the custom-header ACP config. But it would be working on either every 'category' or every 'topic' not just one individual category.
Oh probably should add you need to drag the 'Well' Panel, but add another class="another class" <-- use this in the ACP custom-header config. Also adding a style="height:250px;" .. or whatever you desire wouldn't hurt also