Instead of using List, you could create an image with the same aspect of the list with interactive SpriteText on, that places itself to the position you prefer when you click something, and that places itself out of layout when you don't need it anymore.
We have a list of skins we can put on a character, but they are locked:
Now, when we press on a locked button (in this case the plant) construct2 moves the buttons outside layout, and places the popup at the same position:
Obviously you don't need to move them all, just Pin the objects to another one and move that one.
In my case the buttons are pin'd to the first button, and the popup that appears is made by text and sprites pin'd to the "buy button"
*Sorry for my terrible english
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