Alternately, if you don't want to mess with the font origin point, you can have an event like
>For each SpriteText >Move SpriteText to (Button.X - SpriteText.CharacterWidth/2) , (Button.Y - SpriteText.CharacterHeight/2)
assuming that Button's origin point is in the center and the button text is one letter. Add a multiplier for more letters, and an instance variable for multiple buttons.