I'm pretty sure Balsaman did on his first machine (if it wasn't him, I know I've seen someone do it). I think you just need to use some type of straightedge to align them. I got some IKO rails on Ebay I plan to do this with, and I noticed while looking at their literature that they sell special sets made to butt end to end, I guess maybe they have tighter tolerances. But for a homebuilt router, I don't think you'll have a problem. One thing you want to do, is that if the rails are different lengths, stagger the joints.