Couldn't stun the wraith officer with 4-6 electro nades just now. I tried softening him up before throwing them, 2 plasma shots and 1 laser shot, followed by the nades. Not sure if it matters but I'm pretty sure he was pretty close to death as the next hit from anything would kill him. Here's the vid of my final attempt, did about 3-4 more tries prior.
http://www.twitch.tv/thecockmasterxxx/b/414995140?t=163m0s