Add a new flag in "Enlighten World Flag" visual

Hello!

I'm currently working on a new project and I have a country filter. So I used the Enlighten World Flag visual object to make the country flags appear. 

In my list of countries, I have the Benelux (Belgium, Netherlands and Luxembourg) and I have an internal flag that I would like to show.

Do you have an idea of how to proceed?

Thanks a lot!

Jean-Ri