I've used Fett with the Jetpack in regular JA FFA (of course it doesn't actually WORK, it's just the model), but I don't know how to make it happen again. It may simply have been a fluke... normally he appears without the jetpack on his back.
Yes, the only consistent way to use it is to play Siege_Desert or use cheats.
i seem to get Boba's jetpack now when i die by anothers hand with a saber in any ffa since the patch realeased. it doesn't work, and is a bit buggy if you put on give all cause theres some z fightning but otherwise it is a nice detail.