Changing cdata on image handles in GUI for plot

In my gui, I am saving my image in a handle so that I can call it from different functions like this: handles.img = i1. Then I can imshow(i1) to show the image. However, I also want the user to be able to draw on the image using imfreehand. Sometimes I will want to change the image in the background but keep the imfreehand drawings on the figure. Is there a way to change the cdata on my handles.img so that it just changes the image in the background and keeps the imfreehand lines?