I have done the same as DocHeb bolt 2x4 or 2x6 to the end of the fence use two 2x4's and sandwich the fence between them. I use three bolts, top, bottom, and middle. Then loop the chain around my drawbar and attach to the top and bottom of the 2x4. Put the tractor in low range and stretch. I have stretched up to 50 feet of fence at a time and as little as 10 feet. It depends on the lay of the land. On flat land I can stretch 50' with no problem.
If the land is rolling which alot of mine is I will stretch the fence lock the breaks on the tractor and go to the low points and make sure I can push the fence down and not have the wire so tight that it pulls the steel post out of the ground.
If you are uneasy about stretching with the tractor you can attach the come-a-long to the draw bar and chain. But the 2x4 method works great and I can bolt the 2x4's together faster than I can slide a metal bar through the fence.
I am sure you will hear from other people on this site that have other methods just as good or better.