Addapted from a product called AirChair:
www.airchair.com/
Originated out of Oz if I recall.
They've since been adapted to tow-in surfing and kiteboarding too. There are photos somewhere online. The guys do use snowboard bindings to handle the extra leverage on the ankles though. It's just a welded stainless construction so quite heavy too. Simply trim the ride height with the board angle and if you do it aggressively enough you can get quite a good jump out of it.
Edit: found that somewhere
www.kiteforum.com/viewtopic.php?t=6363
