Talvez você esteja procurando Configurar o controle remoto de sessões de serviços de área de trabalho remota :
You can monitor the actions of a client logged on to an RD Session Host server by using remote control from another session. Remote control allows you to either observe or actively control a client session. If you choose to actively control a client session, you will be able to input keyboard and mouse actions to the session. You can warn a client that you want to remotely control their session by choosing to display a message on the client that asks permission to view or take part in the session.
O artigo se aplica ao Windows Server 2008 R2, mas já vi um mecanismo semelhante já usado desde o Windows Server 2003 R2.