You can customize the #loadIndicator CSS and attach it using the Resources section of the in5 dialog.
You can also attach a folder with your custom image inside, then reference it in your custom CSS, e.g.,
#loadIndicator {
background-image:url(../resources/myimage.gif);
width:100%;
height:100%;
}
More CSS would be required to get it exactly the way you want it, but hopefully this will help to get you started.