ClientRpc method does not get invoked

Hi,
In a multiplayer scene, how can i manipulate its gameobjects in a way so that only specific players can see these changes? I though ClientRpc would be the way to go, however the according method is only called on the client that is NOT the host at the same time. Any suggestions?

[Server]
void Update()
{
// find gameobject to be manipulated; find target client
RpcManipulateCube (tmpObj, playerID);
}

[ClientRpc]
public void RpcManipulateCube(GameObject targetCube, string targetPlayer)
{
// apply changes to target Object on a specific player
}

You would need to send a message to the specific client connection. Check here: http://docs.unity3d.com/Manual/UNetMessages.html