I can think of no truly "dummies" way of doing this. The easiest I can think of is to:
- Take out %image and replace with a New Widget Area (See the New Widget Area section in the theme options).
- Find a slideshow plugin that supplies a widget
- Create slideshows for each page
- Put all the slideshow widgets in the new widget area
- Install and use the Display Widgets plugin to hide/show on the pages in question.
There are some "ifs" here. You need a slideshow plugin that allows multiple widgets such as Nextgen and you will have to style the slideshow to "fit" the header area. For instance you may have to use overflow: hidden etc.
Other than the above you would have to code some conditionals in the theme itself which is certainly not the "dummies" way.
Maybe I'm missing the obvious though and someone has a simpler solution.