It really doesnt seem possible to convert a nitro engine to gas.
Like rcaeroguy says, you would need a sparkplug and ignitions system. not to mentions that gas has a lower flash point than nitro, so if you spilled some on a hot cooling head, theres a chance it would ignite. Plus, nitromethane creates more energy when it burns than gasoline, so you would need to run a high octane fuel and you still wouldn't have as much power.