There's lots of modifications for advertisements, but you can do it manually.
Code:
<if condition="$foruminfo[forumid] == '2'">your advertisement code goes here</if>
That will show the banner in just the forum with the id 2. So you could do that for each banner and just place them one after the other.
It may be $forum[forumid] instead, depends on where you use the code.