How to insert code inside certain div in ckeditor rather tha

I am trying to create buttons for ckeditor that will add rows and columns of contents to the editor using 960.gs grid system.

I need a way to insert the generated code into certain div that already exists in the editor window not just at the cursor.

For example, We have this code in the editor:

<div class="container">
  <div class="grid_12">
    <div class="inner">
    </div>
  </div>
</div>

When I click my button, This code is generated:

<div class="grid_3"></div>

I need the generated code to be inserted into the div with class (grid_12). Whatever the position of the cursor is.