You can replace the half ghee and half oil with the full quantity of oil or ghee.
To save the gas, When you are roasting koki for first time, roll out next one in small circle. When you are rolling the first one second time, cook the second one for first time.
When you are cooking first one for second time, roll out the second one in big circle.
Following this way every time atleast one koki will be on your griddle and gas will not get waste.