fuslage twist

Are both sides of the part twisted?

Before you go after your model with a hair dryer, is this a model of a single engine airplane? If the model is a single enging airplane you need to consider "p-factor." All single engine aircraft have the vertical tail surfaces set at an angle to compensate for this phenomenon. http://wiki.flightgear.org/Understanding_Propeller_Torque_and_P-Factor Since the model you are working on is 1/32 scale, the angle of the vertical surfaces might be readily visible while not visible on a smaller scale model in 1/48 or 1/72 scale. Just a thought.

I bow to Don, his idea on heat is better than mine.

I would jig it up to apply torque in the correct direction, apply the heat, and then let it cool slowly. I am afraid any sudden cooling may rewarp it.  I get best results holding it perfectly still while it cools.  I had a recent experience with wings warping when I tried to increase the temperature of my drying box.  I got the warps out by clamping to pieces of MDF and putting it back in the drying box for an hour, then removing it from box and letting it cool slowly in ambient air.  Needless to say I returned the temp of the box back to 100 degrees from the new 115 F.  I may support any cantilevered parts while drying, like wings, in the future, even at the lower temp.

Might try a hair dryer or heat gun, warm it up to almost too hot to hold (without deforming).  Hold in position and cool under cool running water.

Other wise sounds like cut apart and reposition and reglue. 

Another thought would be to let some thin liquid cement wick into the seam and soften it up, hold in position until it dries, then rework the seam.

Model plastic has a pretty fair degree of 'memory.' Barring the ability to add some serious internal bracing...heat or cutting are the only things that will overcome it.

Whichever way you decide to go...good luck!