Guncraft Blocked and Loaded

You can only freeze enemies by killing them in either the Racing or Lava Survival game type. Start up a match of Lava Survival with your partner, 60 minute time limit and infinite resources turned on, on Flatlands, and shoot a block out from under them so they fall into the small gap. Crouch down and aim at their head, than rubberband the RT button on your controller down. Have them do the same. This way you're constantly firing, and they eliminate their spawn shield as soon as they unfreeze after 10 seconds.

Have this go the whole game, on a 60 minute match the lava will reach you around the 13 minute mark, scoring you around 77 freezes every 13 minutes. Make sure your partner occasionally wiggles their LS to avoid being kicked for idling.