Here's a few things you can try, depending on your desired result:
1. doStop unit;
doStop should keep a unit in one place, until ordered to move on again (or possibly until is AI makes him move again).
2. unit disableAI "MOVE";
disableAI "MOVE" will definitely keep a unit in one place. He can still shoot. This is good for behing a low wall, or behind a window. If you put a guy behind a window, facing out, the following will keep him standing up, and not moving anywhere else:
unit setUnitPos "UP";
unit disableAI "MOVE";
To allow unit to move again, use this command: unit enableAI "MOVE";
3. If you want a civilian to be a member of opfor, but without an opfor leader then do this:
a. Create your civilian unit
b. Create an OPfor unit with "Probability of Presence" set to zero
c. Group the civilian unit to the Opfor unit
When the mission starts, there will be no Opfor unit, but this civilian will act as an OPFOR unit, and will be treated as an OPFor unit by all other units in the game.