This is probably too complex for a simple mod, but I always thought a low tech item like a good old megaphone would do the trick.
Have a soldier 'use' it and issue a command to go to a location or hold position. Then every civilian in a certain radius from the speaker does an intelligence check, perhaps modified by the soldier's rank as some sort of perceived level of authority, and if they succeed they stop panicking and follow the order.
Naturally the any aliens in the area are affected as well after performing a check to see if they understood what was being said. If they succeed they treat the source of the noise as a location to inspect. If not then assume it is the tortured wailing of some earthling and carry on.
You could think of it as a less forceful and non invasive version of the Psi amp used to calm instead of cause distress.
