Add elements like size box, or spacer, to widget by blueprint

Hi! It works perfectly, but, would it be possible to set the spacer´s size to “fill” from blueprint? I can set a custom size, like in the images you posted, but, it would be nice to change that setting in order to get the center align like is described in this post: [UMG] Arrangement of the children in Horizontal box - #6 by maxxburman