I haven't justified purchasing a long rail for ripping plywood and was always looking for a way to facilitate joining/aligning two rails. In a perfect world, the rail connectors would fit the rail slots snugly and by default, the two rails joined together would be aligned perfectly. Unfortunately, this is not practical from a manufacturers point of view.
Inspired by the adjusters on my unisaw miter gauge, I performed a relatively easy mod to the rail connector to make the alignment of 2 rails easier. I drilled 4 holes through the connector sized for a 1/8" nylon rod. The rod I had was slightly oversized so I used a .128" drill. Then I tapped the holes approx. half-way through for 8/32 set-screws. Assembly was installing the set-screws so the were just flush and inserting the rod from the other side and trimming to length. The set-screws act as pushers on the nylon rods which extend through the other side and eliminate the free-play between the rail and the rail connector.
As of yet, I've only modified one connector and have been using it in the bottom slot, the same profile that the saw uses for alignment. I haven't tested it enough to say that the rails will align perfectly with this mod but I can say it is a huge improvement. The only change I might recommend is to use nylon-tipped set-screws instead of the nylon rod/set-screw set-up.
I know this might be a little more metal-working that some may want to perform, but with about $10 in supplies and a hand drill you can eliminate most, if not all, the tweaking required to get the rails aligned after assembly.
edit to correct pics