This is something I have planned to do on my website. I haven't tested the idea yet, but you're welcome to give it a try.
You can create an EZ-Page (must support running php, check forum for "php inside ez-pages"). That page would run a DB query to check for $_SESSION['customer_id'] and cross-reference that customer's orders history to see if he purchased that product. If it was purchased, the EZ Page loads a video hosted on your server using flowplayer or some other player (obviously YT and similar sites are not an option). If the product isn't found in that customer's order history, you have the <else {}> available... :smile:
I'm sure this is a spartan way of doing this, but it should work... Plus, it's not that complex to write it... :wink: