Smooth "transition" for partial stacks

In the facebook group I just saw a partial stack that had a very rough transition from the in-focus to the out-of-focus areas. That often makes those partial stacks look unnatural and is particularly true for stacks shot with low f-numbers.

Would it be possible to get a smoother transition by slowly fading the last images of a stack out? Options would probably be to give them less opacity or blur their edges.