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Sorry, there are no current hacks that I am aware of. As it is right now, they are either on or off, or deleted from the database.
There may be some 3rd party scripts you want to try, but I'm not up to date on the latest ones. Naturally, these would run outside your XOOPS environment, but have code that you can use in your theme.html to show and rotate your banners.
Maybe others here on the forums may have more information, my knowledge in this area is quite limited. A good place to start might be www.hotscripts.com