I believe Construct 3 doesn't have that feature. Can't you just use a Sprite instead of an ImagePoint?
I know that's not the question, but it would work for most of the things.
Basically you could Set position of Sprite to desired X and Y, then Pin the Sprite to the object it needs to be on. When you need to change the ImagePoint position, you Unpin the sprite, set position to round(random(.., ..) and Pin the Sprite to the object again.