Jim is right, a pic will help, is it kinked, or just a gradual curve?
It's just a gradual curve. It's actually hard to see that it's misshapen until you really look at it closely.
If it is a gradual bend, you will have to over-bend it to get it to be straight after the tension is left off.
When bending it, you do not want to crush the tube into an oval shape. a hardwood dowel up the middle of the tube is the best way to go... using a copper pipe up the middle is a bad idea... both will go oval together. You might want to sand the dowel down to as close of an exact size as possible.... mounting the dowel in a large chuck and 60 grit paper will let you remove stock fairly quickly and evenly... hopefully you know someone with a woodworking lathe, that's the best tool for the job...
It seems like the dowel Idea is a popular one. I o know someone with a lathe, so I'll probably try this first.
Thanks everyone for the advice!