That's not possible by any means
To use two or more cards on the same system, they need to be the same and they need to be in SLI
He can use the GT630 for extra monitor ports, but if I am correct they will still be rendered on his main graphics card.
Don't worry however, the fps drop will be in the <1% range anyways. Nothing to worry about when you have a game on one monitor and the others sitting idle.