How do i make some products non-browse-able?

I am wondering how I can do the following:

On my website I have a standard product list of items and I want people to browse them, add them to the cart, and checkout and pay for them.

I also have some special promotional items that I do not want to have show up in any browse-able product lists, or in any catalog. So you can think of a preferred client getting a coupon for a free gift. It is not a gift we show anywhere on the site, but if the client comes to my homepage and enters their secret code in a form box, they are taken right to a checkout page for that secret item. Ideally (but not required), this would really take them out of the whole shopping cart flow as well - i.e., when they enter a valid code they go to the checkout page for that item and do not have an option to go back and add more things to the cart. These special items are sometimes free and sometimes I need to charge a nominal tax amount at the checkout.

Really wondering if this type of customization can be done and if so, how to go about setting it up.

Thanks