[Plugin: Top Commentators Widget] Change Gravatar To User Avatars

Hey, I’m using the Top Commentators Widget plugin and it comes with the option to display gravatars.
Hardly any of my users have gravatars as through the reistration process on my blog users are allowed to upload custom avatars.
Does anyone know how to modify the current gravatar code so that it calls for the users avatar associated with their email address instead?.
The code I use in my comments template is this:

<?php global $user_email ?>
<?php echo get_avatar($comment, '40'); ?>

The above code succesfully retrieves the avatar associated with the commentators email address.
Any ideas on how to utilize this in the Top Commentators plugin instead of using gravatars?
Any help is appreciated,
Thanks.