Here's a way to do it just in index.php, without modifying the core code or db or anything. though this might seem hacky, it's rather simple. it will slightly throw off posts-per-page counts and won't be completely hidden from other sections, but bear with me.
- make a category called 'feedback'. This way, the post will be isolated away, and still people will find your feedback page immediately...
- make your 'feedback post'. make a note of what post number it is. make sure it is in the feedback category.
- set a variable at the top of index.php called something like $feedbackPostID. set it = to the post number.
- inside the $posts loop, the very first thing you should do is:
if (empty($p) && $post->ID == $feedbackPostID) continue;
That should be it. You can now link to the post directly, list_cats will include the (singular) post in its list, and people can click on it to get to the commentable area, and in theory you could expand this to other posts.
Now, the 'right' way to do this, and not screw up page counts, etc., would be to have some kind of new post field called post_hidden (or something), and add a rule to the main query (or queries more appropriately) that tests for post_hidden != 1 IF not querying a singular post (empty($p) and other matching checks). Or, add a new post_status called 'direct' that basically does the same thing (except by adding it to post status, it will 'disappear' everywhere until you add new exception code to all the other queries in the code... ;) ).