Add a shortcode to tinymce that echoes bloginfo's values. (example: [bloginfo key='template_directory'])

wp_get-bloginfo-shortcode.php

function my_bloginfo_shortcode( $atts ) {
   extract(shortcode_atts(array(
       'key' => '',
   ), $atts));
   return get_bloginfo($key);
}
add_shortcode('bloginfo', 'my_bloginfo_shortcode');