Just read this on the BF3 Reddit from someone who got it to work on the Xbox.
"Alrighty guys. I have the results!
You can do it on xbox, but you have to be in the passenger seat. What you will need to do is simply press A (X) until you are in the passenger seat. Press and hold the Right Bumper (Knife button) and then immediately leave the vehicle. As soon as you leave, let go of the leave vehicle button while still holding knife button. It may take a few tries but it'll work eventually. NOTE: You can do this RU or US but you must be the passenger."
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