Customizing wp_list_categories ?

How can I use wp_list_categories() (or a similar command?) to produce the following output:

<li>
    <a title="December 2011" href="http://...">
        Dec 2011
        <span class="postcount">27</span>
    </a>
</li>

What I currently get is

<li>
    <a title="December 2011" href="http://...">
        December 2011
    </a>
    (27)
</li>

i.e. I want to trim the Month, want the end of the link at the end of the content, and want a span around the postcount.

Any help?