UNet Parent System

In my FPS, I have a command that spawns a prefab and sets it's parent. It works fine on the host but on the client it's not parented. I tried calling an RPC when it is spawned, but that wont work, because this game is going to be one of those games where anyone can enter/leave a match at any time. So how can I set an object's parent across the server, and for all clients? I use this code to spawn the prefabs-

     [Command]
     void Cmd_EquipWeapon(NetworkHash128 id){
         GameObject go = null;
         ClientScene.prefabs.TryGetValue (id, out go);
         if(go != null){
             GameObject wep = (GameObject)Instantiate (go, Vector3.zero, Quaternion.identity);
             NetworkServer.Spawn(wep);
             wep.transform.SetParent(Gimbal.transform);
             wep.transform.localPosition = Vector3.zero;
             wep.transform.localRotation = Quaternion.identity;
         }else{
             Debug.LogWarning ("Couldn't equip weapon: Asset ID invalid! AssetID = " + id.ToString ());
         }
     }