I got an idea.
If you played Far Cry series games, you probably remember that ability to throw a rock somewhere in order to distract enemies.
So the idea is: you can add a command to throw a rock (stealth_throwrock) that you can bind on a key. Every time you call this command, you throw a small rock that makes sound and all enemies go and check what was the noise. This would help to sneak through an enemy outpost without being detected, or simply to lure them into danger. Like, if you can't walk through somewhere because there's an enemy watching, you can throw a rock, so enemies turn around to look where did that come from, while you quickly sneak past them.
The rock must disappear after some time, of course. It would make some lags if a lot of entities would exist on the map at the same time.