This can be done on the first spitter you encounter.
Chapter 5: Pure Lighting.
You'll enter a room where Rani will comment on the spitter, something along the lines of it being new. You'll also be on a ledge looking down at it.
Here, thanks to Goots 88 and F77Bloky for confirming, you can stun the spitter with
&
which makes it a bit easier to sneak round.
Drop of the ledge and loop round to the right, sticking close to the right hand wall. I wasn't especially careful, and didn't get spotted. Continue round the pillar, until you can see the spitter. You need to clear a little bit of gunk at the edge of the platform the spitter is on.
I then walked slowly, as close to the wall again, until I was behind it. Then you just RT to grab and pull, and the achievement should pop straight away.
If you do get spotted you can let the spitter kill you, or sit in some gunk to restart the checkpoint.
Not sure if the spitter can become unaware again if if spots you, if someone can confirm?
If you having any troubles let me know