Try this... remove the tip end leaving the tip bolt (alternately, depending on construction,removing the tip may leave a screw hole). Attach a string or wire to the hole with a screw or the bolt with a nut (it's usually a standard thread... a good DIY store can tell you the size.)
With a fine grade of steel wool or very fine sandpaper, lightly remove the glaze finish from the shaft area that is warped. It's best to have it down to the bare wood. This is easily replaced with a polyurethane spray after completing the process. Next, remove the butt bumper. This, again, will leave an attach point. Wrap a small gauge wire around a heavy object, such as a large hammer or other heavy iron tool... (a brick or two will do as well). Attach this to the bumper end. Find a location to which you can attach the tip end that will leave the cue free to hang staight up and down without touching anything else.
Place the cue in a hot shower for 10 to 15 minutes and hang from your chosen location. Every day as often as you can, spray the shaft with warm to hot water. This should produce a straightend shaft in a week or two, depending on how often you dampen it...
Best of luck!