You do it from seat manually, change ignition, shift fuel tank etc...
Start on gas by crank or battery, run it warm and shift fuel when running.
Here it is no point anymore either, but at the time Engine kerosene was about half price to gas here so it was a point to it then.
I doubt you can get it at all anymore. They say you can mix diesel with 25% gas and get the same property's in fuel, but there is no point as it is almost same price.