Front foot on the bolts, back foot on the flat of the tail. There's a little lift to be done just to get your board up into the barrier, but you shouldn't be aiming for a half assed ollie kind of wallie. You basically just jump vertically, suck your damn knees up a-la shit for brains' method, and let the board follow your feet. There's a bit of a lean back as well, so your board can travel up the barrier, and your weight should shift naturally from tucking and hitting the barrier. I've clipped my feet plenty of times forgetting how tall they really are, so really jump.