You know that you don't need the crossfire bridge for mining right?
Unless he's running Windows and doesn't have or want to use dummy plugs.
Crossfire hurts your performance when mining. People use dummy plugs because they have no choice. When I had 4x crossfired it was constant problems.
Crossfire hurts when its enabled. Crossfire cables being plugged into the cards doesn't mean crossfire is enabled. I have the bridge plugged in on my main pc but have crossfire disabled in the driver control panel. Works just fine...