Driving diesel cars for years, whenever I went to a state with mandatory attendants, they always wanted to pour gasoline in them.
First don't exaggerate some gasoline in diesel will destroy the engine.
In the past, when fuel additives were not available, truckers during winter would add couple gallons of gasoline to their tanks to prevent fuel gelling.
Than make it simple. Gas cans are red, diesel cans are blue or whatever.
Small diesel generators don't exist and even if you find one in acceptable size, that will be $$$$$
