Since env_screenoverlay is disabled in Portal 2, is there any way to emulate its functionality?

I vaguely someone somewhere suggesting env_sprite, but I'm not sure how I would go about keeping the sprite in front of the camera.

The effect I want is for a coop map. The players go through a pretty easy test, Wheatley gets angry and rips half the chamber away, merging it with another and leaving the floor unstable. Eventually the floor breaks and the bots fall into another, stable chamber. During, or after, the fall, I want to add a broken glass overlay to both player's screens, which will get 'fixed' when they get to the assembly machine.

Yea, it's 100% gimmick and isn't necessary, but I want to try it out.

You have to reenable it in a mod or overridding the pak01_dir vpk,
Isn't the security camera in coop when you do a gesture an overlay?