Link rather than import images in Keynote

I'm creating an interactive prototype in Keynote using images of views as slides and add clickable areas which link to other slides. So far so good. But I've found that the maintenance of the prototype is quite cumbersome since I seem to have to re-add all images that I adjust, in other words: images that I've added to the Keynote document aren't updated when I make changes in the original image file.

Does anyone know how to get around this?