Make product modifier pre-fixes 'mandatory'

Right now, the way we have it set up, our modifiers have 4 pre-fixes ("Add", "No", "On the side" and "Sub"). When a customer wants to add a modifier (such as avocado) hitting the pre-fix "Add" is what charges them the cost of that item; we run into issues with our online ordering because customers are clicking on only the modifier (example avocado) but they are not being forced to click any of the prefixes, therefore they aren't being charged the cost of the modifier.
Once the customer has picked their modifier (avocado, bacon, cheese etc), we need to force them to pick a pre-fix so if adding, they get charged for that modifier.