There is a trick to make it "animate".
Create item icons in number equal to all of the animation images. Like this:
1: |o |
2: | o |
3: | o|
Create item for each of the image. Create a periodic event that for each unit that has item 1, 2 or 3 in inventory "transforms" it into the next one. So delete the item, create the next one and put in the same slot in inventory.
An "animation" can be actualy done.

There will be a problem with moving the item, so make a turned-off version and let it be changed with left-click.