I've recently had to solve a similar problem on a personal project, a King Air B200.

On any side view of an aircraft that has washout, the designer has to decide what to show on the drawing, since there are actually an infinite number of sections along the span. So, they usually just show the root, or the root and tip. On a multi-engine plane, the nacelles are somewhere along that line, but at what angle...?

Dihedral is a factor, too, especially if the nacelles are not circular. Why? Because (at least on the King Air) the nacelles house the main landing gear, and in the front view, they are vertically aligned, although the wing passes through them going from low to high, inboard to outboard. (See the first image.) When I started thinking about how to solve this with precision, it gave me a headache, but eventually I came up with a solution.

If you have an airfoil plotter, it will be handy. The rest is "low-tech". The next series of images shows how I solved the problem on the King Air, which you may be able to adapt to your needs.