i can't see them helping you with anything that you would be doing if you wore them around on, say, an average school day. the only thing you'd do with them on would be jump and do spins on and off curbs, which ankle weights wouldn't do anything for. sure you wouldn't jump as HIGH, but the spinning would be just as easy because the guy above me is right, theres a difference when you've got a hundred and something cm of weight to swing.
putting them on and hucking stuff on the tramp, or off a diving board would DEFINITELY help, but as far as rail tricks go, ankle weights would only make it easier for you to get the height to hit urban rails....
sick idea though, at first I was pumped to try it out and i may invest for my trampoline this summer :)