Making entities invisible even in Spectator mode

Spectators see all things with an invisibility effect or tag as if they were semitransparent. To get around this you need to use an entity that doesn't render, even without invisibility.

Prior to 1.8.2 this could easily be achieved with a WitherSkull, like this:

/summon WitherSkull ~ ~ ~ {direction:[0.0,0.0,0.0]}

When WitherSkulls have no motion they did not display. Unfortunately they "fixed" this in 1.8.2.

After 1.8.2, there isn't really a good way to do this.

The best I can come up with is summoning a WitherBoss, and then constantly setting its Invul tag (which changes its size) to a certain value:

/summon WitherBoss

/entitydata @e[type=WitherBoss] {Invul:10000}

Unfortunately, as you can see, the particles, shadow and boss bar are still very visible. IMO this is worse than just having a translucent baby chicken.

This is now fully possible as of 15w33a, using the AreaEffectCloud entity with a radius of 0:

/summon AreaEffectCloud ~ ~ ~ {Radius:0,Duration:216374}

The only way to see it is with F3+B: