Can you manually add some placeholder animations with empty frames, and set the desired origin point location? Then in runtime select an empty frame and load a new image into it.
In older releases of Construct it was not possible to add frames in runtime. So if you needed to load 100 images, you had to manually add 100 frames in the animation editor.
Another option is to use an invisible "base" sprite for each card (with the origin point in the center), and attach the card image to it using hierarchy.