Curious as to what the group thinks about a method I've tried. I too always thought the threaded rod left a bit to be desired...so I started with a couple of pieces of hardwood attached to the inside of the dropouts using small bolts through the fender brace eyelets. Approximating axle location on the wood blocks, I used a 1" diameter by 3/16" thick grinding stone to carve a depression in them more or less following the seat stay angle. From these crude jigs, I inserted and spread progressively larger Turnbuckles. Due to their right and left threading, the spread was controlled, and equalized, in both directions at the same time. Might not be ideal for correcting a problem, but seemed to be fairly quick and accurate for something straight to begin with. Word of warning, the mechanical device used, (turnbuckle), is no where near as secure as the threaded rod with washers when exerting pressure. Use some type of fail safe in the operation. Zip ties, cable, something looped through the eyebolts and the frame to prevent accident should it slip free. Kind of a long setup initially, but as I said, it seemed to yield good results for me.