Hi Andy,
Best place to practice this trick is to find somewhere where it is cross-off shore to offshore to begin with, usually a sand spit or a point that is flat and sandy to allow an undisturbed airflow over it works best. SO NOT TRY IT IN NORMAL OFFSHORE CONDITIONS as it is dangerous and gusty, a lofting accident is a real threat. The trick is to be able to get the board on your feet VERY quickly as you have barely enough time.
Because you have very little forward speed, you do not go high so to help, you need to take a few quick steps towards the water and upwind to simulate the tensioning of lines and reorientation of the kite to slightly further back in the wind window.
I usually hold my board by the handle with my back hand and keep that hands thumb over the back of the bar to enable you to keep pressure on the back lines and give yourself a good swift turn. Start with about 10-15 feet from the waters edge and have the kite at around 11 o'clock (assuming a port tack start)and then start running towards the water as you turn the kite back to 1 oclock, as you swing up and over the water, take your back hand thumb off the bar and put your board on whilst pulling hard with the front hand to turn the kite back towards the water.
It takes a good location and plenty of practice to get it right. I also used to run my footstraps a little loose when I was doing board offs to make it easier to slip the board on in a hurry.
I hope this helped, good winds,