MANWON,  
I tried your cold method and used some heat to try to straighten a really warped shaft. I am not sure if I was doing this incorrectly or if the warp was too severe.  I went against the advice of "Do Not Add Moisture" and I wrapped the cue in a towel, binded with rubberbands, then used a clothes steamer to steam the towel. Then the high point up, I had placed the cue on books, and added a little weight to the middle of the shaft.  I repeated the process seeing slight results each time.  The final few attempts I had hung  the towel wrapped cue so it was perfectly vertical, steamed more and then let it dry completely like this.  The shaft is now completely straight.  I recognize that moisture can damage the cue more, but as a last ditch effort it worked well.