Hanger Banger/etc- a way to protect your £10 dropout with your expensive frame.
Right, how to straighten perfectly without the proper tool. Do you have an old cup-and-cone axle? (you can use the whole wheel but it's easier with a loose axle). The rear axle (and maybe the front, I don't know) uses the same thread as mechs do. So, take your axle, with one nut on it, thread it in (sticking out to the outside of the frame) til the nut butts against the hanger.
Now, you can see how squint it is fairly easily. But to make it easier, get a suitable straight edge and stick it in the dropouts, so it sticks out beside the exle (I use a bit of M10 threaded bar but anything straight will do, it's just simpler). Now you've got 2 parallel lines, and a nice lever to do your bending with. Could not be easier once you've got that.
Don't do it too often on an alu one- I take the approach that I'll tweak one if it's a wee bit off but I won't do wholesale straightening.