(I think this may be a symptom of not implementing something else...) In a vanilla crafting bench, and other inventories, you can move stacks to your hotbar using the number keys whilst hovering an item. Could this be made to work in the various Grids?

Also grabbing half a stack of items does not work the same as in other inventories ( This is why I suspect refinedstorage does not implement some existing code for doing both these inventory things ).