Whesley McCabe says:

Generally, GERC is a widget-only plugin, but you can manually call the function by adding this code to your template files where you want GERC to appear:

<?php gren_reco( array() ); ?>

You don’t have to define array() but if you wanted to customize the way the comments are output, the array should be defined as:

Defined:

• before_widget is the wrapper for the output and defaults to <div>
• after_widget is the closing tag for the wrapper which defaults to </div>
• before_title is the wrapper for the title as defined in your widget options – which is currently set to Recent Comments – and defaults to <h3>
• after_title is the closing tag for the title wrapper which defaults to </h3>

Generally speaking, you could set before_widget to something like
<div class="mostRecentComments">
and you could use CSS to style the way GERC is presented using the class definition
.mostRecentComments { }
and you can style the listed comments using the ID definition
.mostRecentComments ul#gren-reco { }

Since you’re using a function defined as a widget, the title, number of comments, and gravatar size are all defined by the widget control. If you change any of these settings for the widget in your sidebar, it will also change for the manually inserted function. There is currently no way to separate them.

Hope this helps!