that's what I'd figure.. was it actually ever done successfully outside of the movies?

Most B-29 engine fires were "induction fires" and a couple of "put-outs" were used to extinguish the fire. Problem was the accessory section at the rear of the engine! If it caught fire, then you have a major problem, even though we had 4 "fire extinguisher" bottles we could blow and most times it worked just fine. I had only one induction fire in 924 hours in the old bird and we "blew" it out with throttle!
Having said that, Boeing engineers, coupled with engine manufacture engineers, designed a special "dynifocal" made from magnesium, with the plan in place, with an accessory fire which you could not put out, the dynifocals would burn in two and the engine would actually fall off the wing. I only saw one aircraft land at Tinian with #4 engine hanging down at about a 20 degree angle, because the two top dynifocals burned into, but the bottom ones did not, hence the engine crushed the dynifocal extention arms and was resting against the fire wall when they landed.