Minecraft – How to rotate the ‘FallingSand’ blocks with /setblock

Please see

Minecraft Empty Chests Command Block

as I think this answers you question.

Let's say for example your equipment chest is supposed to contain a notch apple, a gold sword, a bow, and a stack of arrows. The command for that would be /blockdata X Y Z {Items:[{id:322,Damage:1,Count:1,Slot:0},{id:283,Count:1,Slot:1},{id:261,Count:1,Slot:2},{id:262,Count:64,Slot:3}]}, replacing X Y and Z as appropriate. There's a lot of stuff going on in that command, but essentially, you are changing the data of the chest to contain the specified items. It's the same concept as using /setblock to spawn a new chest with these items, except instead of replacing the chest, you're overwriting its data.

To answer your question, you can't summon sideways falling sand, but you can create an illusion of movement by rapidly summoning and destroying a falling sand block with a slight change in horizontal direction. Just set up a clock to a line of command blocks and it should do the trick.