Sure.. just run a line to a pressure regulator and have a hose that connects to the car.
(That's a very gross oversimplification of it, but it can be done.)
Another benefit of CNG powered vehicles is they still run internal combustion engines, so manufacturers would'nt have to do extensive retooling to produce the vehicles.
The biggest drawback is the pressurized tank of CNG you'd be driving around with. But if Honda can build a car that meets safety standards there's no reason Ford/GM/Chrysler/Nissan/Toyota (well, maybe not Toyota, as they're still figuring out how to get their cars to stop) can't do it.