It's not really safe to do, *but* I won't say I've never done it. For example, when my car had a dead battery on the way to Florida I refueled the car (twice?) with the engine running.
Just make sure that you don't get a spark across the filler neck and the nozzle. It's a good idea to ground yourself to the car and the nozzle first. I can say that I can count the number of times that I have done it on one hand.