How to add an "Open Package" button that adds a fee to the order?

[Edrax]

Hi! I want to add an "Open Package" option in PrestaShop's checkout, and if the user selects it, an additional fee (e.g., 2.2 USD) should be automatically added to the order total.

What would be the best way to implement this? I've seen a few possible solutions:

• Creating a hidden virtual product
• Using a dedicated module for extra fees
• Manually modifying the code (checkout/cart)

Has anyone implemented something like this before? What solution would you recommend? Any suggestions are welcome!