For variable product: make one set of attributes not required

Hi,

I have a variable product on my website, that has 3 attributes: Color, Size and Buttons. The price of the product depends on the color and the size. But I need to show users which variation has buttons and which don’t. Button attribute can has multiple options.

e.g: A product with the Color: Red and Size: Small can has the Buttons attributes: 2 button, 3 button. But an other combination of Color: Red and Size: Medium does not has any buttons.

WooCommerce does not initiates the variation unless all the attributes are selected.
My question is: How do I take the buttons attribute out of the variation and use it to just for appearances based on Color and Size attribute selection?