i let my friend have a go on mine, n while he was walkin like a smop as you do when you start out one fell out, n i found it started to make a really loud well a bock noise when ever it was stood on, but its really easy to push back in if you still have it, im sure any sort of plastic/rubber would help, maybe a cut up credit card, use the one you have to cut the credit card in the correct fashion and voila, a new spacer.
ok probably not a good idea... what do you say pro-jump people?