I found Desert Strike 14 is a little easier since the angles are shallower.
Bean the first guy hard in the head to knock him over, then abort the explosion. Now toss two more so that they hit the guy lying down and bounce into the standing person (who should remain standing), aborting each time. The guy lying down should now be enraged and the standing guy will need one more hit. Gently toss a grenade at the standing guy, which will enrage him, fall down and detonate, killing them both and netting you the achievement.