The old shift-click problem - attach a hopper to a chest, or a button to a dispenser, or place a rail on the hopper... on PC you do this by clicking while holding shift. In the midair, you can use shift+space to arrest descent and place your block against a container instead of opening the container.
On PE I found I can do this by entering the sneak mode, when landed. But if I'm building something high in creative mode, levitating as normally in creative mode, the sneak button vanishes. Building a floor to stand on just to be able to crouch becomes seriously cumbersome.
Is there some trick to placing blocks against containers in PE when flying, equivalent to PC's shift+space?