I was facing the same issue and came up with this completely hackish solution... It works though :)
add_filter( 'get_avatar', 'so_14088040_localhost_avatar', 10, 5 );
function so_14088040_localhost_avatar( $avatar, $id_or_email, $size, $default, $alt )
{
$whitelist = array( 'localhost', '127.0.0.1' );
if( !in_array( $_SERVER['SERVER_ADDR'] , $whitelist ) )
return $avatar;
$doc = new DOMDocument;
$doc->loadHTML( $avatar );
$imgs = $doc->getElementsByTagName('img');
if ( $imgs->length > 0 )
{
$url = urldecode( $imgs->item(0)->getAttribute('src') );
$url2 = explode( 'd=', $url );
$url3 = explode( '&', $url2[1] );
$avatar= "<img src='{$url3[0]}' alt='' class='avatar avatar-64 photo' height='64' width='64' />";
}
return $avatar;
}
Result:
Of course, this filter is meant for development only.