There is one weird way to do that. I don't know either it is right way or not but it will reverse the order from say ASC to DESC.
In advace theme function a_list($a_list)
foreach ($a_list['as'] as $a_item)
replace with below
foreach (array_reverse($a_list['as']) as $a_item)
This will reverse the answer order. If you want to allow user to sort of them choice than you need to crete a link when user click on that it will switch between these tow sorting. May be using jQuery.
Hope this weird trick may works for you. Give me your feedback hows that? :)