A local cue maker straightened out a shaft for me one time using a unique method. The shaft was noticeably warped, we are talking heavy bend in it. He put it in this homemade tray type holder where he could roll it by hand. Now the end where the tip is had graph paper, and as he rolled it you could see the tip move from square to square. A perfectly straight shaft would stay centered on the graph paper. As he rolled it, he would mark the shaft at the joint where the tip went lowest and then took the shaft to his table saw (a nice flat surface) and lifted up at the joint bending the cue where he had marked it.
He put a lot of bend into it but there was never a snap crackle or pop sound, and after a few times going back and forth the shaft went from having a big bend to a slight wobble. He did say that it may warp back, but after several months the shaft stayed about the same with just a slight wobble.
Come to think of it, I remember him also steaming the shaft before bending it. All I know is it worked and the shaft was a lot better to play with when he was done.