Hey, I've uploaded a new addon called Stack Traceback which will stack all the stuff in the guild bank as expected. It hooks StackBag, so just pressing the button will stack the items.
It doesn't stack them when you deposit the items though. RequestMoveItem is protected, so that's a bit more difficult to do since I can't hook it.
It doesn't do it optimally though, and simply assumes that stackbag wants to stack both subscriber and normal bank if you pass one of the two to it. It could potentially be modified to do so. There'd be an issue of a destination bag, as well as potentially high run time. It also would need some changes to handle the virtual bag.