What I do is put a big button at the end of all the answers that does exactly the same as the link up top. To do that, put the following in your advanced theme (check docs for details):
function a_list($a_list)
{
parent::a_list($a_list);
if ( count($a_list['as']) > 0 )
{
$this->output(
'<p align="center"><input name="q_doanswer" onclick="return qa_toggle_element(\'anew\')" value="Post an answer" title="Answer this question" type="submit" class="qa-form-tall-hover qa-form-tall-hover-answer"></p>'
);
}
}
If you want the button after every answer, you could instead copy the a_list function exactly from qa-includes/qa-theme-base.php and put the output line inside the loop.