Cast resin has 'memory' and will return to it's original shape if dipped in hot water. There is a video somewhere showing this, a warped piece of resin being dipped into hot water a couple of times and straightens out.
Of course, this is easy for small pieces and not so easy for large parts but I have used this technique many times myself with 100% success.
EDIT: here's a link to the thread, but the video link seems to be private now. :
http://www.network54.com/Forum/47211/thread/1211989082/Best+way+to+straighten+out+warped+resin+parts-