Oh it was nothing flash. Installed a roof beam support in the shed, hung a bar of it at a height whereby when in chicken loop you almost lift yourself into it with feet just on ground when in the foot straps. Had outside lines running through a pulley each from the roof beam with adjustable knots to tighten or slack these.
start with board a little back, simulate a jump (head to my left) then you have until you swing back to get board off then back on. Quickly teaches you body position to get the board back on (which is the point most people fail). Add in your tic tacs, flips etc. even rotations. That muscle memory doing it hundreds of times comes handy when you are 20-30 feet up.
but word of caution, nearly gave myself a hernia. So be careful on stomach muscle fatigue !! Also use a **** board and make sure nothing is valuable in your shed when practising kick flips etc!! Anyhow all to no avail now don't really do that stuff anymore. Foils came along and with it big kites were sold.
On the lad ...
eventually went a round 12 foot trampoline (50 bucks yeeha) then tied the bar to a rope with a length of rubber and slackened line all as per the wakestyle training vid someone posted here. Also added in a bigger spring to make sure the bar really pulled away from him during the pass.
he spent a week training on it (no wind) and then two days later made his first three 313 air passes... all in a row.
Love it when a plan comes together.