How to fill a block with an Armor Stand

An ArmorStand is an entity, not a block. Use /summon to place it. To rotate it's leg use the /entitydata command. Here's a screenshot for what you want:

The lowest Command Block has the following command:

/summon ArmorStand X Y Z

Instead of X, Y, Z put your desired coordinates. For an "upgraded" ArmorStand use this command:

 /summon ArmorStand ~ ~ ~ {Invulnerable:1b,NoBasePlate:1b,ShowArms:1b}

This command will summon a invulnerable ArmorStand without a base plate, as seen below:

The upper Command Blocks have these commands:

/entitydata @e[type=ArmorStand] {Pose:{LeftLeg:[310f,0f,0f]}}

/entitydata @e[type=ArmorStand] {Pose:{LeftLeg:[0f,0f,0f]}}

It doesn't matter which one you put where, but I put the upper command into the left one. These commands will make the left leg of all ArmorStands go back and forth. If you want only eg. the closest ArmorStand to "kick", use @e[type=ArmorStand,c=1] instead of @e[type=ArmorStand]. For other Entity selectors, go to the wiki page.

The repeaters are set to max delay, except the one diagonally to the Stone block, which is at minimum delay. You could set the clock (at the bottom of the screenshot) to a different delay, but the uppermost repeater should be set to the same delay as the clock repeaters.
The thing under the Piston is a Comparator, and the Piston is sticky.