No, I'm afraid it's not quite Sir Paul on a bungee cord jumping off some kind of high-up structure, but something else quite cool related to the other phonetically identical word -- mega-games studio Bungie. According to the past-Beatles members' Twitter, he's lending his talents to the creators of Halo, but what exactly is he working on?
Well, don't expect him to be motion-capturing for some sort of alien creature, you can instead expect him to be in the music studio composing some sort of epic score -- but that of course depends on what Bungie are even working on. While 343 Industries has taken the reigns for the Halo franchise with the upcoming Halo 4, Bungie has apparently been working on something called 'Destiny'.
Whether that's the name of some kind of exotic dancer; the actual name of the game, or just a working title, rest assured, if it's anything like past Bungie titles, with an added sprinkle of Sir Paul McCartney's musical genius, I'm sure it will be quite something. [Forbes]