Is there a reliable way to takedown sitting enemies?

I've just infiltrated the Harvester's Hideout and I'm trying to Ghost my way through. This means lots of non lethal takedowns. Standing enemies are pretty easy to lure wherever I need them to be (so that they're out of visual range of their buddies before I beat their face in) but sitting enemies are a problem.

Example:

Even though I'm right behind him, the game does not allow me to perform a takedown while he's still sitting. If I move in front of him, he sees me. If I want him to stand up, I have to get out my silenced 10mm and shoot something in front of him so that he gets up to investigate the noise.

Is there a way to reliably perform takedowns on sitting enemies such as the one shown here?

Solution 1:

I'd use the stun gun (for which you have low-ish ammo, sadly) in occasions I can't approach an enemy safely without alarming them. A dart gun to the head works too -- the guy will fall after a few seconds, but won't raise the alarm himself. Usually with sitting enemies, they are not looking aside, so you might be able to approach them quickly and take them down before they sound the alarm, but it might not work in every situation

Alternatively, from the looks of it, you might be able to jump-crouch on the bunk the guy is sitting on and take him down.

As others suggested, you could also sneak by cloaked and, uh, have your way with him.