A little misapprehension: I have vertical drop-outs. We have an interesting thread at the German Pedelecs Forum about stretching a bike frame by heating up and using a thread rod. Due to springing back of alu or steel you have to overstretch the frame. The heating up works with a hot-air gun.
http://www.pedelecforum.de/forum/index.php?threads/alu-hinterbau-aufweiten.27803/
http://www.pedelecforum.de/forum/index.php?threads/alu-hinterbau-aufweiten.27803/