Selectively use skybox for ambient light contribution

I'm working on a scene where I've got an interior (cockpit) and exterior (visible via windows in cockpit). I don't want the cockpit's interior to have its ambient value coming from the skybox, but I want the exterior scene objects to take their ambient contribution from the skybox. What is the best way to specify certain materials to use the skybox and others something else (ideally a reflection probe inside the cockpit, but maybe just a color)?