For your further research pleasure, there's a sticky thread... and at least one other thread on how to get FB prints flat.

I personally like this trick: Participate in a print exchange. Some prints will come to you perfectly flat. Ask the person who sent you flat prints what they did.

http://www.apug.org/forums/showthrea...ferrerid=38808

http://www.apug.org/forums/showthrea...ferrerid=38808