How to allow program to use hidden category without exposing it to customers?

I use another plugin to display cart messages (as well as per-product messages) that populate based on the category of the product.

To explain with my real-world example:
I have cuts of meat that are categorized under Pork, for example.
So lets say I have Pork Chop Steaks, and Pork Bones for Example.

I have a category for Pork with a sub-category of “Steaks” and another sub-category of “Bones”

Not all products under “Steaks” or “Bones” are created equal, so we have some items which are priced “Per Pound” – meaning we won’t know the exact weight or price until the item is weighed on a scale (when we fill the order later)

The other items are packed “Per Package” with a known price. (We don’t need to weight it to know how much to charge)

I want to use a “hidden” category called “Priced Per Pound” so I may group products together from various different parent categories, and use THAT hidden category to trigger the Shopping Cart Messages that the other plug-in displays.

I don’t want customers to see that category “Priced Per Pound” but I do want them to see the products and the message that the 3rd party plugin produces.

The issue I am having:

When I mark the category “Priced Per Pound” as “Hidden” the popup messages from the 3rd party plugin stop working.

If I un-hide the category, then the 3rd party message appears as expected.

Is there a way to resolve this?

Thank you so much!