ya i started using a trampoline to practice on last year and it actually works. i started busting wake to wake 3's after only a couple of days of practice on the trampoline.
get some old shoes and screw them to an old skateboard then grind off the tips of the screws. i also tied a rope to my wall in my backyard to learn rope control.
check out my website if you want to, some wakeboarding clothing there.
http://www.wakecell4.com