It's possible but I wouldn't say it's easy. You can just set them up as unit of a 3rd faction that has no movement available (0 move range, 0 attack range, etc). That will make them attackable by other unit. You can get them to do an aoe damage to all nearby unit by adding the code in DestroyRoutine() in Unit.cs. The tricky bit is make sure the turn sequence to still work correctly if somehow the explosion has took out some of the units.