Yes, like just about every topic, this one has many threads in the archives showing it has been bandied about previously. Sometimes, though, someone has a new observation or a new method to share. So.....what the heck.
I have resorted to using cardstock shims, I have planed and sanded roadbed so that it superelevates the outer rails, and I have slipped the bottoms of risers supporting spline roadbed outward so that the spline surfaces are titled just enough to tilt the tracks. There are many methods, and all can be made to work with some care and skill.
I usually caution people wanting to superelevate that they should be careful to minimize it. I don't mean don't use it on your curves, or on most curves, or anything like that....heck, it looks really great in photos if you get it right. What I mean is that 'getting it right' is unlikely if you overdo the disparity between the rail heights at the apex of the curve. IOW, less is more. Just a bit, just enough that you can say, "Aaaawwww....that's so cool."
I mean maybe 1 mm, perhaps as much as 1/16", but I would not go any higher.
Test your elevated curves, too. Make sure they work will all your equipment in both directions, and reversing, too. Only then should you ballast.
-Crandell