In this case you would use Ditto and use the
&tplFirst to define the first item template, then use
&tpl to define the second item and finally use
&tplLast for the final item template.
That is a good question since that is not covered in the tutorial (the author is not as bright as he thinks he is

)
In practice you would have the &tplFirst be something like:
<div class="grid_4 alpha">
<p>[+content+]</p>
</div>
The &tpl like this:
<div class="grid_4">
<p>[+content+]</p>
</div>
And the &tplLast like this:
<div class="grid_4 omega">
<p>[+content+]</p>
</div>
Then you would put the ditto call in the footer div:
<!-- Footer -->
<div class="grid_12" id="footer">
[[Ditto? &tpl=`tplChunk` &tplFirst=`firstTplChunk` &tplLast=`lastTplChunk` ...<remaining ditto params>... ]]
</div>
<div class="clear"> </div>
Edit: I had mislabeled the tpls, corrected to read
&tplFirst and
&tplLast