ride in them alot, or put some bottles in the toes and the entry part of the bindings to help stretch them a bit. whenever i rebuild my bindings, it usually takes about a month or so of three times a week riding to break them in. hope this helps.
beer bottles work pretty good.....i would leave them in for about a weekend. Just make sure you got plenty of extra beer so you don't have to end up tipping your wakeboard to get a swallow.