I know of at least one person in the UK who has converted their older Toyota Prius to run on gas (I don't recall if it was CNG or LPG), and will do conversions for others.
I suppose that you could do the same with the Honda Civic Hybrid and convert it to natural gas instead of gasoline. Converting a hybrid to use natural gas instead of gasoline would be much easier to do than to convert a natural gas vehicle to add in a hybrid drivetrain...
Honda Civic CNG had a fuel economy equivalent of 24mpg city/36mpg highway (similar to that of the gasoline-only standard Civic), but thanks to full-cycle production/sourcing analysis it ranks as the greenest vehicle currently available in the US according to the American Council for an Energy-Efficient Economy. It is followed closely by the Toyota Prius at 48mpg city/45mpg highway, and the Honda Civic Hybrid at 40mpg city/45mpg highway.
http://www.greenercars.org/highlights_gr…