How would I make an entity stay frozen on the spot, mid air (no AI)?

So there are two ways to achieve this:

• MCEdit, or
• 20hz /entitydata.

For MCEdit:

1. Go into your world, and place the sand with blocks underneath them.
2. Open MCEdit, and find your world's level.dat.
3. Delete the blocks under the sand.
4. Save, quit, don't block update the sand.

For commands:

1. Create a fill clock.
2. Attach the following command to the clock: entitydata @e[type=FallingSand] {Motion:[0.0,0.04,0.0]}
3. Spawn the FallingSand.

Disclaimer:

I don't have screenshots for any of this, nor have I tested it, but it seems as though it should work.

Teleport your falling sand constantly to an Armor Stand which has {Invisible:1b} and {NoGravity:1b}.

In Vanilla, you can put a barrier under it.

There are multiple ways of doing this without commands, by using "transparent blocks" (like lily pads for example).

• Place a body of still water 2 blocks below the desired height of your sand block.
• Place a lily pad beneath each desired spot for your sand blocks
• Place down the sand on each lily pad. You will notice the sand blocks "float" one block above each lily pad.
• Important - do not break the lily pads! Because the lily pads are "touching" the sand blocks, interacting with them directly will cause the sand blocks to fall. Instead, place a solid block beneath each lily pad.
• Clear out your "scaffolding" (the blocks you placed to contain the water) and voila!

This can also be done with vines.