kingcrunk

odr_m9611, the following code should work for you:

add_action('init', 'ads_rewrite');
function ads_rewrite() {
  global $wp_rewrite;
  $queryarg = 'post_type=ads&p=';
  $wp_rewrite->add_rewrite_tag('%cpt_id%', '([^/]+)', $queryarg);
  $wp_rewrite->add_permastruct('ads', '/ads/%cpt_id%/', false);
}

add_filter('post_type_link', 'ads_permalink', 1, 3);
function ads_permalink($post_link, $id = 0, $leavename) {
  global $wp_rewrite;
  $post = &get_post($id);
  if ( is_wp_error( $post ) )
    return $post;
  $newlink = $wp_rewrite->get_extra_permastruct('ads');
  $newlink = str_replace("%cpt_id%", $post->ID, $newlink);
  $newlink = home_url(user_trailingslashit($newlink));
  return $newlink;
}

Let me know if it works!

I’ve come up with a solution to this, finally!

Here’s how I’m using it:

Permalink structure =
/ Custom Post Type Slug / Post ID / Post Name Slug /
aka
http://iloveomfg.com/tracks/%post_id%/%postname%/
which outputs
http://iloveomfg.com/tracks/377/flux-pavilion-bass-cannon-flufftronix-nolibs-club-edit/

—–
The trick was to replace the string %cpt_entry% with the already built-in WP permalink string %postname%. Doing this eliminates the 404/Page Not Found errors altogether, and also allows you to edit the post slug in the post editor like you can normally.

Here is the final code which I used, based on dpchen’s earlier post in this thread.

Add the following to functions.php:

add_action('init', 'tracks_rewrite');
function tracks_rewrite() {
  global $wp_rewrite;
  $queryarg = 'post_type=tracks&p=';
  $wp_rewrite->add_rewrite_tag('%cpt_id%', '([^/]+)', $queryarg);
  $wp_rewrite->add_permastruct('tracks', '/tracks/%cpt_id%/%postname%/', false);
}

add_filter('post_type_link', 'tracks_permalink', 1, 3);
function tracks_permalink($post_link, $id = 0, $leavename) {
  global $wp_rewrite;
  $post = &get_post($id);
  if ( is_wp_error( $post ) )
    return $post;
  $newlink = $wp_rewrite->get_extra_permastruct('tracks');
  $newlink = str_replace("%cpt_id%", $post->ID, $newlink);
  $newlink = home_url(user_trailingslashit($newlink));
  return $newlink;
}

The great thing about using this type of permalink structure, and the specific reason I am doing it is because it allows you to make easy short-links of your urls… for instance:
http://iloveomfg.com/tracks/377/
works the same as
http://iloveomfg.com/tracks/377/flux-pavilion-bass-cannon-flufftronix-nolibs-club-edit/

However, for some reason, this does not work:
http://iloveomfg.com/tracks/flux-pavilion-bass-cannon-flufftronix-nolibs-club-edit/
For me, it displays an archive of all my custom post type “tracks”.

Hope that helps you guys out!