I've used the method involving a long bit of threaded rod with washers and bolts the inside of each dropout and turning equal amounts (not sure that's really necessary, but that's what someone suggested. It worked for me, but was sort of a pain because, as FBinNY suggests, one side moved out further than the other. This meant I had to put the side that went out further down and put pressure on the seattube until the spacing was equal. Took several tries to get right. If I had it to do over again I would either have bought the 2x4 or paid the bike shop the $50 they wanted to do it, but the day I wanted to do it the bike shop was closed and I am car free so transporting a 3 ft length of threaded rod and some washers home from the hardware store was easier than a longer 2x4. Also, I got two pieces of threaded rod, so I could use them to align the dropouts when I was done. That worked ok.