1) Drat, that would be a really useful thing to have.
2) The attached image should illustrate what I mean. The vertical lines represent the line segment. The way it happens now is the top one. It starts at the first point and add rail segments until it goes past the end and then slices. The second one is how I'd like it to work. Basically it would calculate how far it would go over and then offset the start position by half that distance. Then slice the beginning and end.
3) Another idea crossed my mind while thinking of the default rail segment. There are two options tile and scale. What about a third option. "Tile Nearest" (or something like that) Basically find the number of whole segments that would fit into a line segment, then scale all of them to fit the space. This way you can tile but still always end up with complete rail segments and nothing sliced off except the angle on the ends.