Curve superelevation has been covered many times on these forums, but here's a condesed version of what has been posted before:
There are about as many ways to superelevate model curves as there are modelers who build them.
To name a few, from least to most drastic: masking tape, cardstock or balsa under the outer ends of the ties, wedges or strips of ??? under the ballast former (cork or foam roadbed), tipping the whole cookie-cut structure by manipulating the risers (only possible for cookie cut subgrade on risers over grid or L-girder structure.) Folks who build on splines can slope the spline structure from one side to the other, or tip it.
Chuck (Modeling Central Japan in September, 1964)