I've just done this quite easily.
Firstly, install the Improved Include Page Plugin:
http://wordpress.org/extend/plugins/improved-include-page/
Create a new page in your Wordpress install that's going to contain your content. You're probably going to want to hide the page from your site navigatuion so perhaps install something like the Page Link Manager plugin:
http://wordpress.org/extend/plugins/page-link-manager/
Once you've done that, copy one of the default feature-front-*.php files from:
wp-content/themes/thematicfeaturesite/includes/
Perhaps call it feature-front-3.php
Open it in an editor and find these lines:
<h2>Lorem ipsum dolor sit amet consectetur elit adipiscing nunc</h2>
<p>Cras tristique consectetur dui....</p>
Replace the title between the H2 tags with your own wording and replace the <p>Cras tristique...</p> line with this:
<?php iinclude_page(202); ?>
Obviously you'd have to swap the 202 in brackets with the number of your new page.
Then edit wp-content/themes/thematicfeaturesite/functions.php
Find this part:
$rand = mt_rand(1, 2);
include "includes/feature-front-$rand.php";
Remove the first line completely and edit the second to read:
include "includes/feature-front-3.php";
Once all that's done, I think it'll work as you wish. It does here anyway :)