Hello,
Maybe this will be a little different from what you want but we think that the content tags can help you, have a look on this
blog article
for better understand this feature (and see a concrete example).
{hkshow bought="109"}content{/hkshow}
In details, this tags will help you to add a
link in your product description and
only being display, if the login user have already purchase the required item (targeted from his Id, here "109").
Now, the point is to inform (in the product page and the confirm order email) the customer that in order to reach this link he must go back to the product page itself
Hope this can help you to achieved your needs.
Regards