How did you beat the one where you call into an alley with 3 guys scattered in the corners? That one and the one you mentioned were the only ones I couldn't beat without shooting.
I went invisible, jumped down, grabbed the guy in the far left corner, threw him at the guy in the far right corner (at this point he is the guy on the left) while moving towards the guy closest to spawn, then as I neared said last guy I started spamming grab on him. Common mistakes I make while doing this are not being close enough to the first guy to grab him, doing an aerial takedown on accident thus losing my projectile, and not being close enough to the final guy to reach him before I lose.
Edit: Found an alternative route. I went invisible, jumped on the guy in the far left, raced towards the guy in the middle during the fraction of a second between the kill and the enemies noticing me, then closed the rest of the distance and threw him at the remaining guy.