Hide the add to cart button for already bought/licensed commerce files

Would be nice to hide or just to show as disabled the add to cart button for already bought/licensed commerce files.
This is a feature request I already highlighted in the DC Forum itself (http://www.drupalcommerce.org/node/1202), and following what there adviced I went through a little more in the Commerce Stock module, to get its approach and borrow some ideas (when the product is out of stock, the add to cart button is disabled, as shown in the attached screenshot).
For the Commerce File module a similar approach would be nice, as it is (might be) useless to enable the add to cart button when the user looks to a product display that reference a product to which he as the license file granted ... and that he can already simply download.
I am not so skilled with Drupal module developing or hacking to be able to produce a patch yet, but I think this is something that might integrate with the user/account access logic built for the commerce file field display (and download): when this is shown for the user, it means he has the license file granted for that file product. At the same time the (eventually) Add to cart button display should be hidden or at least disabled, highlighting that it is useless for an already bought (or in the cart) product file ..
Would be really nice, and even nicer if it is an optional behaviour checked or unchecked in the Commerce File administration form ...

Thanks a lot!