We used to tie a waterski rope to a tree and simulate flips and rolls on a trampoline. I don't think the action of a jetski really transmits the same though. The physics of it are just so different.
Yea I've used trampolines in the past for wakeboard training. Working on muscle memory for handle passes on spins, etc. plus, it's just so incredibly fun!
I've thought about using a wakeboard handle as simulating the handlebars, but being attached to a tree doesn't help a whole lot when you're doing a backflip (like a jetski backflip).
My goal is to instill muscle memory for doing spins and flips while taking limbs off. And who knows, maybe superflip training
I've been thinking of pool noodles, but not sure about a structure that could keep them together beyond some sort of welded yada yada.
As always, the best practice is doing it on the actual sport (wakeboard/jetski), but learning things on a trampoline is a proven training mechanism for many pro wakeboarders, usually with less risk of injury.