1) place the civilian on the map
2) group him with an east or west side unit (make sure the civ's rank is lower than the E/W unit)
3) put this in the E/W or Resistance* init field that is grouped with the civ:
Deletevehicle this
then the opposite side will fire at them; (ex: if you grouped it with a west unit, east will shoot at him and vise-versa)
*if you group the civ with Resistance, under the intel screen (click the cloud/sun at the top righthand corner) there is a "Resistance friendly to:" area at the bottom. Make sure it is "nobody" if you want both sides to shoot at them. You can use it to determine who will shot at them:
Friendly to:
West- east will shoot at him
East- west will shoot at him
Nobody- both sides shoot at him
Everyone- no point, he's safe from both sides