Field mapping custom value

Is there a way for example with a hook to add custom values to the field mapping value dropdown?

The problem:
We have many products and not all of them have a short description or description.

The idea:
Add a custom value for example: My Own Description

Which would be a result returned by a php function from functions.php
If the short description is empty return my custom text + the product name.
If it is not empty return the short description.

The hook should have the $product_id, so I can read all the information from the product.

Thanks.
Peter.