Thank you for raising this topic. lunarplexus and me had a long discussion over this, and have come to a solution, wherein, you would need to map two Gas Stations next to each other. One dispensing Normal Fuel, and the other dispensing CNG. The reason this would work out best is that, as and when Waze activates Gas Prices in India, the prices are Brand Specific.
Like you mentioned, Delhi has numerous Gas Stations which vend different brands of fuel at one Gas Station. To adapt Waze to such a situation, we will map two Gas Stations at the same physical location. The first will carry the normal fuel Brand, the the Second will carry the CNG brand. Every fuel station which dispenses CNG and normal fuel will need to have an additional Gas Station mapped solely for the purpose of showing the CNG prices to Wazers. It will help to name these CNG Gas Stations with "CNG" mentioned at the end of the nomenclature.
I trust this is clear.