They are added as council (3 of them) missions. So, it's highly scripted. You get a new operative who's only difference from all the other is that he looks and sounds different. No other special abilities. Perhaps the title slingshot comes from the fact that it will give you access to a technology you have to research later in the game. To me, this only serves to make XCOM even less of a proper XCOM/UFO feel. The whole game to me was hyped into tricking me it was the holy grail of XCOM/UFO gaming when in fact it's just a very generic game that just happens to look good. Yes, I was deeply disappointed.