Sometimes - popping them in the freezer reaaaaally doesn't work.
Some peeps have had results popping them on some forks with laggy bands pulling the buckled area back in again (over a long period of time), there's a thread over at the Museum with a bloke that's designed a wooden press (in combi with some light steamage) to get em back to true.
Best bit of advice though - if you don't want to take the chance of them not straightening out, spend a few more bob and get a good pair