I use shims to get the wing on straight and then make the saddle permanent by filling it with epoxy and micro-balloons.

1/8" isn't much, but if you can make it 0 then you're better off. That slight amount may only need a piece of cardstock for a shim. This page doesn't tell you how to get the wing on straight, but it will make it stay straight after you get it that way even if you use shims like I do.

http://www.airfieldmodels.com/wing_saddles.htm