Aligning an overlay to existing GUI elements

I'd like to align an overlay ("instruction pane with arrows pointing to gui elements") to existing GUI elements... The GUI elements are placed relative to screen-size. The problem with simply putting a texture element on top is that with just a single graphic rasterized at X x Y it might not be the right-size, i.e., the arrows might not be pointing at the right GUI elements..

So, I am wondering what is a better way to put an overlay over existing GUI elements, while having its parts align to the elements.