replacing line 169 of includes > jj_ngg_jquery_cycle.php to:
$newurl = get_bloginfo("wpurl") . "/" . $image->path . "/thumbs/thumbs_" . $image->filename;
$output .= "<img src=\"" . $newurl . "\" " . $image_description . $width_d . $height_d . " border=\"0\" />";
Would be great if this was added as a checkbox option in future versions of the plugin.