Like Bruce said it can be done. Since each truck has a dozen+ balls in contact with the race at once, only one ball will feel the joint at a time. I joined several in my router table build and it is pretty much bumpless, I can hear a tic as I push it over the joint but I can't feel it. At first I carefully milled the end of the first two that I joined and then bolted them down butted together but then the next two I just joined them without milling, I can't tell any difference since only one ball is at the joint at a time anyway.
I am still building and have not tested it on material yet, just running the steppers back and forth, still working on electronics & wiring.
Arnie