Reverse charge mechanism in rent a cab service

Please guide me

A service provider providing rent a cab service under 100% reverse charge mechanism. He got a notice from service tax dept to file service  tax return for Jul 12 to Sep12 and Oct -Mar13, but when I am preparing service tax return there is no option to select category as service provider under full reverse charge, so please guide me whether he has to file nil return or put value of service provided and if yes then how?