To the Point:
Next time you jump, grab some part of the board with your back hand, once you're airborne, keeping front hand pressure on the bar to bring the kite forward again for your landing.
Step One: Jump
As you you are nearing the apex of the jump and you're starting to redirect the kite forward again, take your back hand off the bar.
Bend your knees to lift the board up to your back hand and grab it anywhere you want.
Put both hands back on the bar as you come down from your apex and steer the kite back forward for your landing.
As you get better you will be able to hold the grab longer, because you will be able to redirect the kite perfectly with only your front hand on the bar. Make sure not to put too much pressure on your front hand too early!