Create move waypoint and injure any of the AI up until the point they comment on being injured via the radio. The AI will then occasionally just stop in their tracks, never to move again.

This doesn't happen all of the time, and in my controlled tests where I've placed only a Squad of AI with a couple of waypoints it has only happened once. It does happen, however, in larger missions that I've created and on an annoyingly regular basis, causing missions to completely halt because AI aren't where they're meant to be. These missions however are low on complexity and only involve waypoints and triggers and no scripted elements from myself.