Placing Skulls/Heads Inside Glass Blocks

On the server MCMagic, I found a head inside a glass block at the Japan pavilion (/warp japan) in Epcot. Because this was the first time I have come across that, I have no idea how it was done.

In singleplayer, I tried using a piston to shove a head inside a glass block, but the head kept dropping itself. Then, I tried placing more glass blocks around the first one to prevent the head from popping out, but it still did after I activated the piston. How do I keep a head inside a glass block?

Solution 1:

Player skulls and glass are both blocks, and only one block can occupy the same space.

What you can do is summon an invisible armor stand (which is an entity, not a block) wearing a player skull into the glass block:

/summon ArmorStand ~ ~1 ~ {Invisible:1b,Equipment:[{},{},{},{},{id:"minecraft:skull",Damage:3,Count:1,tag:{SkullOwner:"Skylinerw"}}]}