What an idea sir ji!!!
But towing is not possible, because CNG pipe will not bend during turns, like brake fluid pipes on trolley. However, you can make your own MOBILE CNG pump fill CNG at pump, then park that trolley. You can refill your tank from trolly, but w/o pressureized motor, you won't be able to fill more than half of gas in trolley tank.
You can make a motor which force CNG to transfer from trolley tank to ur car, but again it's not good for SAFETY!!!
Nice ideas, but not suitable for safety reasons