Here's how I did what you try to do in my template...
First off, I disabled the regular showing of the Comments link in place of the "readon" link.
Then, in my template, I inserted this (valid only with JoomlaComment! 3.26 and Joomla 1.5.x) in my frontpage template for an item (default_item.php):
<?php
$joscplugintext = ""; //Do not remove this line !!!
$row = $this->item;
$params = $this->item->params;
require(JPATH_ADMINISTRATOR.DS."components/com_comment/plugin/com_content/josc_com_content.php");
?>
<div class="comment">
<?=$joscplugintext; ?>
</div>
It's not the cleanest way to do it... But the JoomlaComment! code is very hard to follow when you're an outsider.
You might need to just change a bit if you're under Joomla 1.0.x... like:
<?php
global
$joscplugintext = ""; //Do not remove this line !!!
$row = $this->item;
$params = $this->item->params;
require(JPATH_ADMINISTRATOR.DS."components/com_comment/plugin/com_content/josc_com_content.php");
?>
<div class="comment">
<?=$joscplugintext; ?>
</div>
You then just need to place the div in the correct place...
I didn't find any other way to not rely only upon the a.readon tag.
Have fun,
Mehdi