Remove aside post titles from left menu

Hi, I have removed the titles for posts of the format ‘aside’ from the left hand menu by putting some code in wp_includes/default_widgets.php;

if(get_post_format( $r->ID ) == 'aside'){
	continue;
}

But default_widgets.php is a core script so I need to set up a filter to do this. I have looked at adding an extra argument to widget_posts_args to modify the query that gets the posts but I cannot see an argument that applies to the post format. Neither can I find a hook that I can add a filter to once the query has executed.

Does anyone have any suggestions as to how I can remove the ‘aside’ posts titles from the left hand menu?

Yew2.com Green Blog

Thanks.