Add the following code to 'Works Best with Contemporary' and 'Works Best with Contemporary Brochure Pages' layouts (Design | Library | Layouts | Web Page Outer Layouts). Put it just after the 'Sidebar Best Sellers List in a Box' variable:

HTML Code:
<br />
    <div class="sidebox">
    <div class="boxhead">
        <h2>My HEADING</h2>
     <div class="boxbody">
         MY TEXT
This will display it in the same style as the 'Best Sellers' and 'New Products' boxes.

Replace 'MY HEADING' and 'MY TEXT' with the relevant contents for the box. Alternatively, you could create variables (Design | Library | Variables tab) for these items and enter the data in the appropriate field in the interface.