Lets say I have an isometric cube where you can only see the visible (front-facing) edges, and all the lines have a stroke width of 1 unit.

How can I automatically make the outer lines thicker (eg 3 units) and leave the inner lines the same, or at least achieve that visual effect? I say automatically because the wireframes I have are far more complex than cubes. I want to avoid anything that involves manual selection or doing anything by eye (such as painting a background).

Thank you