Can I display submenus in groups, using wp_list_pages?

Say I have top-level(parentless) pages called Fruit, Animals, Cars.

When, say, Fruit is selected I would like to show links to the individual fruit pages below. I would like to be able to dislpay these fruits (or animals, or cars) in several groups with a space between each group of fruits.. a bit like this

+---------------+-----------+--------+
|   Fruit       |  Animals  |  Cars  |
+---------------+-----------+--------+   
|   Apple       |           |        |
|   Kiwi        |           |        |
|   Watermelon  |           |        |
+---------------+-----------+--------+  
|   Banana      |           |        |
|   Lemon       |           |        |
+---------------+-----------+--------+  
|   Strawberry  |           |        |
|   Raspberry   |           |        |
+---------------+-----------+--------+  

You can see in this case, I have roughy divided the fruit by color, putting a space inbetween. For cars or animals it might be another criteria. This criteria does not have to be explicitly named anywhere. So I wondering how to output this list, in a way which requires little techinical ability for the person who enters the pages in the backend.

At the moment I do this to output the child pages:

if( $post->post_parent )
    $children = wp_list_pages('depth=1&title_li=&child_of=".$post->post_parent."&echo=0'); 
else
    $children = wp_list_pages('depth=1&title_li=&child_of=".$post->ID."&echo=0');

echo $children;

But I can’t see a way to limit the output to categories, or something similar, using wp_list_pages. The nearest I can see is the ‘authors’ option, but it doesn’t make much sense to login as different users to create different blocks in the menus…

You could maybe choose to use a tree like that:

• Fruits
• • Color1
• • • Apple
• • • Watermelon
• • Color2
• • • Banana
• • • Lemon
• Level1
• • Level2
• • • Level3

This way, you can, in your theme, hide the second level.

Hope that helps.