Some sort of high-powered automated skeet shooter should be able to handle these. The technology is available and therefore doable.
Actually, there is a system currently in Iraq that can defeat these. Its called the CRAM (Counter Rocket Artillery Mortar). It uses a combination of existing radars and gun systems to shoot these things out of the sky much as you suggest. Instead of a shotgun, the heart of the system is a Navy gatling gun (Phalanx) that was designed to defend against anti-ship missles. These systems are expensive and can’t be placed everywhere, so it has limitations.