You can try using a c-clamp to bend it back in place. You'll need to make yourself something like a jig/tube blocks to hold the tube in place while you bend it. Take something like a 1x3 about the length of your seat stay. Using a jig saw, cut a big sweeping arc starting at one end and going to the other. Take half round file and file the ends of the 1x3 such that it can sit comfortably on the seat stay. Make a tube block that fits the seat stay. Now you can hold the 1x3 against the seat stay, take a big c-clamp with the tube block and position one end of the c-clamp at the bend and the other on the outside of the 1x3. Then start clamping. You can use a straight edge, like a ruler, held up against the seat stay to measure your progress.