Theoretically it's simple. In practice, it's a little different. Servos are pretty stupid and don't know which way the airplane is flying, so they don't care.

If the servo is offset at angle "alpha", then offset the servo arms and control horns by angle alpha, too.

The trick is, making yourself drill crooked holes for the control horn. This is actually pretty easy to make if you use a 4-40 rod threaded through a hardwood insert in the rudder.