I got a modification of your idea, Jack. Grab a Plasma Grenade from the enemy player's supply, activate it, and slam it onto his face hard enough to knock him down. That way he can't chase you, and he flails blindly until BOOM!
Now here are a few more ideas.
-Fotus returns and has a face impalement headbutt assassination.
-Take deactivated Energy Sword handle, press it against enemy's back or neck, THEN turn it on.
-Use shaft of Gravity Hammer to launch enemy up, then spin around and bat him away. He dies instantly, and if you're in an open map, he flies out of the map. If you're in a tight space, he ricochets all over the walls.
-Assassinate Hunters like in Halo: FUD using a grenade. This should only be available on higher difficulties though, so that the higher intelligence of the AI prevents it from being too easy to kill Hunters.