there R 2 possibilities: First you could use mod_rewrite rules for makin simple forwardings on selected pages wich would be the easiest way, but may be not a good choice if the SEO question comes up

The better but also harder way could be copying the autonav block to the block folder in root and make some modifications. the first thing that comes to my head is generating a custom field for pages wich you could parse for a "trigger"...lets say we choose a keyword like "displayFirstChild" and then create a if-else wich asks if the current pages has this keyword. if TRUE then get the getCollectionChildrenArray and pick up the first entry to pull out the URL from it. this URL is the replacement for the given "Image" Page url...just a sketch / hint for further thoughts.

...mmmmh...maybe there is another way: What about creating the first tab row completely from pages that you hide from navigation (checkbox option) an then build it handmade like the footer links. This gives you the freedom for designing it the way you like it but keeps those pages available in the sitemap. the only thing: you have to take care about the URLs. If you change them in the dashboard, you'll have to fix them in the code.

hope this gives you a push in the right direction.