I am cutting some O27 switches down to 30 degrees (from the original 45). This involves removing the curved track right up to the frog, leaving nothing to attach the rail to, since the frog is zinc and not readily soldered. In the past, I have attached the rail to the table in a precarious alignment with the frog using shims and screws.
I think I have found a better way: I drilled and tapped the frog for a 1/2-inch 0-80 screw, to attach a 3/8-inch length of brass tubing, 3/32-inch OD and 1/16-inch ID. (A number-0 screw has a major diameter of .060 inch.) I filed the screw head down to the tubing diameter, which is the same as an O27 track pin, and slipped the rail over it, for a smooth and secure joint.