As soon as you get the nose of your board into the trough or the dip before the wake let off your heelside edge and almost get on your toes while riding up the wake
I find it best to be almost parallel with the wake but not completely.
i have to say i really disagree with these ideas. i think people get the wrong idea about how the tantrum works. check out these pics (courtesy of the natural born thrillaz dvd):
notice the extreme edging in the setup...
now he's starting to flatten out a bit, but he's still on edge - he's nowhere near having his weight on his toes...
now he's coming off the lip. notice he's basically still on edge.