In one Italian cookbook with a recipe for pasta with broccoli rabe and sausage, the author indicates that peeling the outer skin off of the stalks helps to reduce the bitterness. It also seems to me that the broccoli rabe most often available has grown less bitter over time--maybe they're breeding it out of it.
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Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them